What The Iowa Senate Map Looks Like In 2018

By Guest Post

January 4, 2018

The following is a memo written up last year by Nick Conway of the Austin Frerick (IA-3) campaign. It’s an interesting look at how the Iowa Senate map is set up for the 2018 elections, and which districts will be the most competitive. This was written in mid-2017, so there’s obviously been a lot of developments in the time since with special elections and more, but it’s a good starting place to consider the past election data.

Part 1: Overview

The 2016 election was a disaster for Democrats in Iowa. Not only did Trump win the state by over 9 points, but Republicans were able to expand their majority in the State House and, most importantly, win back the State Senate after a decade of Democratic control. The Republicans picked up 6 senate seats, giving them total control of the Iowa state government for the first time since 1998.

Going into the 2018 Iowa State Senate elections, Republicans hold 29 seats, Democrats hold 20, and 1 seat is held by an Independent. Half of the 50 State Senate seats will be up for election in 2018, barring retirements or other vacancies, with Democrats having 14 seats up for election to only 11 for the Republicans. Democrats would have to gain 6 seats to win back a majority, or gain 5 seats to achieve a 25-25 tie. A tie would lead to a negotiated power-sharing agreement between the two parties, a situation that last occurred in the Iowa Senate after the 2004 elections.

The number of vulnerable seats is fairly even between the two parties, giving hope to both sides. If we assume that the 2018 elections will have a moderately pro-Democratic tilt, since the non-Presidential party tends to make gains in state elections during midterm elections, then the most likely outcome is that Democrats gain a few seats while the Republicans hold onto to a reduced majority. However, the range of plausible outcomes ranges from Republicans gaining a few seats to, in the case of a massive anti-Republican wave, Democrats winning a 1-seat majority by sweeping every vulnerable seat. The outcome of the governor’s race could also have a major effect on the State Senate outcome, with the winning candidate potentially providing coattails down-ballot.

This memo will go into more detail about the landscape of the 2018 State Senate elections in Iowa. In parts 2 and 3, this memo will detail the landscape-level advantages held by the Republican and Democratic parties respectively. Parts 4 and 5 will examine the specific vulnerable seats held by each party.

Part 2: Factors That Advantage The Republicans

Republicans have three major advantages over the Democrats in the 2018 Iowa State Senate Elections. First, they have to defend 3 fewer seats than the Democratic Party. Second, the Republicans only have to defend 1 seat that was competitive the last time this group of seats was up for election in 2014, compared to 4 for Democrats. Third, they have the advantage of only having to defend 1 seat that was won by Hillary Clinton in the 2016 presidential election, while all 5 vulnerable Democratic seats were won by Trump in 2016.  However, the latter two advantages may be reduced or disappear if the political environment is not as favorable as it was for Republicans in 2014 and 2016.

The Republicans’ advantage in the number of seats they need to defend is fairly self-explanatory. Democrats would have to pick up half the Republican seats to gain either a tie or a majority (rounding down or up). Republicans can invest more money in each district they are defending, while also having more opportunities to go on offense given the large number of seats the Democrats are defending.

They also have to defend less seats that were competitive in 2014. The Republicans’ closest 2014 victory was just under 2 points in 2014, while their next most competitive seat was won by almost 12 points. The Democrats’ closest seat was won by 4 points, but they also had two seats they won by 5 points, and a fourth seat they won by 9 points. Democrats would require big swings from the 2014 results to win more than 1 Republican seat, which would be very difficult if Republican incumbents run for re-election and are able to hold most of their 2014 base.

Table 1. 2014 State Senate Results with 2012 and 2016 Presidential Results by District

Seat 2014 Senate Results 2012 Presidential Results 2016 Presidential Results
Senate District 9 R +99% (unopposed) R +16% No Data
Senate District 1 R +99% (unopposed) R +27% No Data
Senate District 3 R +99% (unopposed) R +22% No Data
Senate District 11 R +99% (unopposed) R +18% No Data
Senate District 25 R +99% (unopposed) R +9% No Data
Senate District 19 R +81% (unopposed) R +6% R+8%
Senate District 13 R +26% R +4% R+20%
Senate District 7 R +20% D +15% R +5%
Senate District 47 R +13% D +2% D +1%
Senate District 5 R +12% R +5% R +25%
Senate District 41 R +2% D +8% R+19%
Senate District 49 D +4% D +16% R +12%
Senate District 39 D +5% D +7% R +0%
Senate District 15 D +5% D +5% R +15%
Senate District 29 D +9% D +5% R +20%
Senate District 27 D +13% D +7% R +15%
Senate District 23 D +18% D +23% No Data
Senate District 33 D +24% D +25% No Data
Senate District 17 D + 31% D +37% No Data
Senate District 21 D +97% (unopposed) D +19% No Data
Senate District 37 D +98% (unopposed) D +23% No Data
Senate District 35 D +98% (unopposed) D +30% No Data
Senate District 45 D +98% (unopposed) D +37% No Data
Senate District 43 D +98% (unopposed) D +47% No Data
Senate District 31 D +98% (unopposed) D +41% No Data

Editor’s note: these calculations match my data on the Senate races, with the exception of SD 39, which I have Trump winning by 4%.

Republicans also can look to Trump’s strong performance in Iowa in 2016 as an advantage, especially if those 2016 results indicated a “realignment” of voters in rural areas of the state. All 5 of the most vulnerable Democratic seats were carried by Trump in 2016, 4 of them by margins of of 12 points or more, which was greater than his statewide result. If Trump voters in these districts have switched over to the Republican party permanently, and will turn out in a midterm election, Republicans could be in a great position to pick up these seats. In contrast, only one Republican seat is located in a district carried by Hillary Clinton, and she carried that district by less than a percentage point.

However, while these latter two factors may seem very positive for Republicans, they are based on results during the 2014 and 2016 elections, which were very favorable environments for the Republican party in Iowa. If 2018 is a more pro-Democratic environment than 2014, seats that were narrowly won by the Democrats in 2014 may be safe, while seats Republicans won big in 2014 could become 2018 toss-ups given a tough environment. Likewise, voters who supported Trump in 2016 may not turn out in a midterm election, or may be willing to support Democrats, at least in state elections. This possibility has been strengthened by recent polling by the Des Moines Register suggesting that Trump’s popularity in the state has already fallen precipitously. So, while these factors may give Republicans some advantages, they are not guarantees.

Part 3: Factors That Advantage The Democrats

Democrats can be hopeful for two major reasons. First, they can look to play offense in a more favorable political environment than they faced in 2014. In 2014, they were able to hold on to a one seat majority despite large Republican victories in Iowa House races, the Governor’s race, and the statewide Senate race between Joni Ernst and Bruce Braley. The fact that the 14 Democratic seats they are defending were won in that Republican wave election suggests they should be favored to hold those seats in what will potentially be a much more favorable 2018 environment. Generally, the party that holds the presidency does much worse in midterm elections at the federal level, and this usually filters down to the statewide and state legislature levels as well. For example, in the 2010 elections, Republicans were able to gain over 700 seats in state legislatures around the country. With Trump in the White House it’s hard to imagine Democrats not facing at least a slightly better environment than they did in 2014.

Second, of the the two senate classes (those up in presidential years versus those up in midterm years) this is the more democratic-leaning class of seats, at least when looking at the 2012 presidential results. On average Obama won in the 2018 senate seats by 9.7 points, while he won statewide by only 5.8 points. This liberal lean declines slightly if we look at Obama’s median 2012 results instead of the mean results. Obama’s median performance was in Iowa Senate District 39, which he won by only 7.2 points. Nonetheless, this is still 1.4 points better than his statewide result. This slight liberal lean for the 2018 class holds up if we look at midterm results as well, for example the 2014 Secretary of State results. This was an open seat election that was narrowly won by the Republican candidate, Paul Pate, by 1.9 points over the Democrat Brad Anderson. On average, Paul Pate actually LOST in these seats by 2.8 points, so he did 4.7 points worse overall. Similarly to the 2012 presidential results however, in the median seat Pate did better, losing by only 0.1 points, which is 2 points worse than his statewide result.

Whether looking at the median or mean results from 2012 or 2014, the numbers suggest these districts as a whole have a slight Democratic lean of somewhere between 2 and 5 points. This helps to explain how Republicans were unable to pick up any seats in 2014 despite a big win in most statewide elections and a favorable national environment.

However, these factors favoring the Democrats are also not as strong as they may appear on the surface. Noting that they held all these seats in the dismal 2014 environment is a double-edged sword, as it raises the possibility that even in an anti-Republican 2018 environment the Republicans may be able to hold onto their seats just as Dems did in 2014. Additionally, even if Democrats have a more favorable overall environment in 2018, they could be done-in by seat-specific factors. For example, Democratic State Senators who reside in Republican-leaning seats may retire, which could cause those seats to flip in 2018 even if the overall environment is more friendly towards the Democratic party than in 2014. Finally, the Democratic lean of seats is very slight overall, and would likely only make a difference on the margins.

Part 4: Vulnerable Republican Seats

This section will go into detail on the 6 Republican seats that are potentially vulnerable to flipping in 2018. Sweeping all the vulnerable seats while not losing any of their own seats would give Democrats a 1-seat majority in the state senate. As a benchmark to judge the competitiveness of a district, we can look at 4 different election results from the past 3 election cycles:

-The district’s 2014 State Senate results

-The district’s partisan lean in the 2012 Presidential election

-The district’s partisan lean in the 2014 Secretary of State results

-The district’s partisan lean in the 2016 Presidential election

The 2014 state senate results are self-explanatory, as 2014 was the last time this set of seats was up for election. The 2012 presidential election results in each district have been adjusted to show the partisan “lean” of the seat, meaning how much more Democratic or Republican the seat was relative to the state as a whole. So, if Obama won a district by 3 points, that district would have a 2 point Republican lean since Obama won statewide by 5 points. The 2014 Secretary of State result is included because it is the last time there was a competitive election for non-federal statewide office. It was an open seat race, so the dynamics are not thrown off by incumbency, and many seats seem to have a different partisan lean when looking at state elections compared to federal elections. So, despite the Secretary of State’s low profile, the results from that election give us a good reference point in case certain seats have a significantly different partisan lean for non-federal elections.

The partisan lean in the 2016 presidential election is also fairly self-explanatory. Unfortunately presidential results have not been calculated for every state senate district as of yet. I calculated the 2016 presidential results for the 5 vulnerable democratic districts and 6 vulnerable Republican districts, but did not calculate results for the safer seats.

Editor’s note: Pay attention to how they describe what these presidential leans are, as they can be a little confusing at first when you look through the next sections. For example, this memo lists SD 7 as having a D+5% lean, which only means that Democrats did 5 points better than Clinton’s statewide average there. Trump still won SD 7 by 5 points. See my own calculations for these districts in this table of mine below:

District Senator Party Trump % Clinton %
SD 7 Bertrand R 49.0% 44.2%
SD 13 Garrett R 56.1% 36.5%
SD 15 Allen D 53.4% 39.0%
SD 19 Whitver R 49.6% 41.9%
SD 27 Ragan D 54.6% 39.1%
SD 29 Bowman D 57.1% 36.8%
SD 39 Kinney D 48.2% 44.4%
SD 41 Chelgren R 56.3% 37.5%
SD 47 Smith R 45.8% 46.4%
SD 49 Hart D 51.1% 41.5%

Table 2. Vulnerable Republican Seats and Competitive Measures

2014 State Senate Result 2012 President Lean 2014 Secretary of State Lean 2016 President Lean Average Result / Lean Average Lean Only Location
Senate District 7 R +20% D +9% D +5% D +5% R +0% D +6% Sioux City
Senate District 41 R +2% D +2% D +5% R +9% R +1% R +1% Davis / Van Buren / Wapello / Jefferson Counties
Senate District 47 R +13% R +3% R +9% D +10% R +4% R +1% Bettendorf / East Davenport
Senate District 5 R +12% R +11% R +6% R +16% R +11% R +11% Pocahontas / Humboldt / Calhoun / Webster Counties
Senate District 13 R +26% R +10% R +3% R +10% R +12% R +8% Warren / Madison Counties
Senate District 19 R +81%* R +12% R +6% D +2% R +24% R +5% Northern Polk County

Looking at the six vulnerable Republican seats, they can be ranked into three tiers. Tier 1 includes only Senate District 7, which not only has a Democratic lean in both Presidential elections and the Secretary of State election, but may also have a retiring incumbent. Tier 2 includes Senate Districts 41 and 47, which have fairly even partisan landscapes and would likely be toss-ups in a mildy pro-Democratic environment. Tier 3 includes Senate Districts 5, 13, and 19, which are all seats that lean towards the Republicans but would still be vulnerable in a wave election.

Senate District 7, located in Sioux City, is by far the Democrats’ best opportunity for a pickup. Compared to the state as a whole, it leaned 9 points towards the Democrats in the 2012 election (it was won by Obama by 15 points compared to 6 points statewide), 5 points towards the Democrats in the 2014 Secretary of State election, and 5 points towards the Democrats in the 2016 presidential election.

Despite this Democratic lean, in the 2014 election it was not particularly competitive, as the incumbent Republican state senator, Rick Bertrand, won by 20 points. This was a Republican wave election, which likely helped Bertrand, but it also suggests that he is a strong incumbent. Luckily for the Democrats, Bertrand has suggested he will not run for re-election in the 2018 election. If Bertrand retires, and assuming a moderately favorable or even neutral environment, Democrats would be favored to pick this seat up. However, the seat is not so Democratic that it is a guaranteed pickup, Republicans could still hold it with a strong enough candidate or weak enough opponent, or if Bertrand changes course and runs for re-election.

Senate District 41 was the only Republican seat decided by less than 10 points in 2014. Incumbent State Senator Mark Chelgren won the seat by less than 400 votes. The seat leaned towards the Democrats in both 2012, when Obama won the seat by 8 points, and in 2014, when Brad Anderson (D) won the district in his Secretary of State race by 3 points. However, in 2016 the seat swung huge towards Trump, who won it by 18 points, despite winning statewide by only 9 points.

Luckily, even in the 2016 elections these voters showed they were willing to vote for a Democratic candidate, as Dave Loebsack, Democratic congressman for the 2nd District, cruised to a fairly comfortable victory of just over 7 points. In Jefferson County, he won by 18 points, winning by 5 points in Wapello County, while he lost Davis County by 4 points and lost Van Buren county by 16 points. Far more votes in this district come from Jefferson and Wapello counties, which Loebsack carried, than the smaller Davis and Van Buren counties. This suggest overall that, at least for Loebsack, the district was still a swing-district at worst. If a Democratic candidate could replicate Loebsack’s results or even come close, they would likely win the seat, but they will have to win many of the Trump-Loebsack crossover voters. Nonetheless, Trump’s strong results suggest that the seat could be moving in the wrong direction for Democrats.

District 47 is in some ways the inverse of District 41, as election results suggest the seat may be moving towards the Democratic Party rather than away from it. District 47 is the only Republican district that was actually won by Hillary Clinton (by less than a point), giving it a lean of 10 points towards the Democratic Party in 2016. By contrast, in 2012 the seat was won by Obama by only 2 points, giving it a slight Republican lean in that election.

The seat stretches across Eastern Davenport and Bettendorf, and is one of the wealthier state senate districts in iowa, with a median income 20% higher than that of Iowa as a whole.  This probably contributed to Trump’s weaker performance here, as higher-income suburban voters swung less towards Trump than other groups. Due to Trump’s weak performance in this seat, Democrats could have success “nationalizing” this seat in the case of an anti-Trump wave. Democrats would also be helped if incumbent State Senator Roby Smith decides to retire or run for the Iowa 2nd congressional district against Dave Loebsack. Smith won by 13 points in 2014, so a big swing would be needed to take him down.

This is a seat that leans solidly, but not overwhelmingly, towards the Republican party. It leaned over 10 points towards the Republicans in both the 2012 and 2016 presidential elections. It had a smaller lean of only 6 points towards the Republicans in the Secretary of State election. In 2014, incumbent Democrat Daryl Beall lost by 12 points to Republican Tim Kraayenbrink. Beall was the only incumbent state senator to lose re-election in 2014. Given that even with the advantage of incumbency, Democrats still lost by such a wide margin in 2014, this is likely a seat that would need a true anti-Republican wave or a Kraayenbrink retirement to be competitive. The seat is also in a more rural area, the sort of area that has been moving away from the Democrats in Iowa.

At first glance the 13th district seems to have a strong Republican lean. Julian Garrett and Donald Trump both won landslide victories in the district. In the last few presidential and senate elections the district been about 10 points more Republican than the state as a whole. However, in state elections for governor, state treasurer, and other executive offices it has a much smaller Republican lean of around 3 points, and on certain occasions it has even leaned more democratic than the rest of the state. Solid wins by two recent Democratic statewide candidates provide a blueprint for a win in the district by a strong Democratic candidate.

State election results also suggest that the district may have a higher than average number of “marginal Democratic voters,” who usually vote Republican but are willing to vote for the right Democrat. The highest percentage of these marginal Democratic voters are located in working-class small-town/rural precincts. These precincts generally had huge swings towards Trump in 2016, while also having a high percentage of protest votes for third-party candidates. Focusing efforts on campaigning in these small towns with a strong populist message may produce the highest “bang for your buck.”

Senate District 19 is likely the toughest of any of these seats to capture. Democrats did not even bother to run a candidate in 2014, although one Independent candidate did run and got 18% of the vote. However, the district, centered on Ankeny and encompassing much of northern Polk County, has been steadily moving toward the Democrats over the past three election cycles. In 2012 it leaned toward the Republicans by 12 points, which dropped to a lean of 6 points in the 2014 Secretary of State election, and finally 2 points in the 2016 election. Polk County was one of the few areas where Hillary’s vote total did not drop precipitously in Iowa. This may be a similar situation to District 47, where a backlash against the Trump administration could pay dividends. However, Democrats will definitely need a favorable environment, and of course will have to actually field a candidate to have a chance at winning.

Safe Republican Seats

Table 3. Safe Republican Seats and Competitive Measures

2014 State Senate Margin 2012 President Lean 2014 Secretary of State Lean Average Lean
Senate District 25 R unopposed R +15% R +13% R +14%
Senate District 9 R unopposed R +22% R +21% R +21%
Senate District 11 R unopposed R +23% R +26% R +25%
Senate District 3 R unopposed R +27% R +22% R +25%
Senate District 1 R unopposed R +32% R +29% R +31%

There are 5 other Republican held seats up in 2018, but at this point none of them look particularly vulnerable. Democrats did not bother running candidates in any of these seats in 2014, and they all had Republican leans of greater than 10 points in both the 2012 Presidential Election and the 2014 Secretary of State Election. The only seat which seems like it could be competitive if everything went perfectly for Democrats is Senate District 25, which has an average lean of only 14 points towards the Republican party, while the other 4 seats all lean 20 points or more towards the Republicans.

Part 5: Vulnerable Democratic Seats

Table 4.  Vulnerable Democratic Seats and Competitive Measures

2014 State Senate Result 2012 President Lean 2014 Secretary of State Lean 2016 President Lean Average Result / Lean Average Lean Only Location
Senate District 29 D +9% R +0% R +0% R +11% R +1% R +4% Dubuque / Jackson / Jones Counties
Senate District 27 D +13% D +1% R+5% R +6% D +1% R +3% Franklin / Cerro Gordo / Butler Counties
Senate District 15 D +5% R +1% D +4% R +5% D +1% R +1% Eastern Polk / Jasper Counties
Senate District 49 D +4% D +10% D +1% R +3% D +3% D +3% Clinton / Scott Counties
Senate District 39 D +5% D +1% D +2% D +9% D +4% D +4% Keokuk / Washington / Johnson Counties

The Democrats have a set of five seats which are vulnerable in 2018. Democrats were able to win all these seats in 2014, so if the Democratic incumbents from these seats run for-reelection and the environment is more favorable than in 2014, they should be favored in every seat. However, if incumbents retire, or if the environment is similar to 2014 or 2016, the Democrats could be in trouble as none of the five seats have a strong Democratic lean. Additionally, Trump won every one of these vulnerable districts, and all but one seat became more Republican-leaning in the 2016 election relative to the state as a whole.

Senate District 29 leaned towards the Republicans by less than a point in 2012 and the 2014 secretary of state election, but by nearly 11 points in 2016. Nonetheless, the incumbent Democratic senator, Tod Bowman, was able to win re-election by 9 points in 2014. If Bowman runs for re-election he should be favored, although the districts massive swing towards Trump should be worrying. If Bowman retires, this would immediately become the Republicans most enticing prospect.

Long-time Newton mayor Chaz Allen ran for and won the open seat in Senate District 15 in 2014. He has indicated he will be running for re-election in 2018. The district leans slightly Republican at the presidential level, with Romney doing 1 point better than his performance statewide and Trump doing 5 points better. But the district leaned Democratic in the 2014 Secretary of State Election, and given the Democrat’s advantage of incumbency and what will likely be a more favorable environment than in 2018, this seat should be viewed as leaning Democratic.

District 39, located in the suburbs of Iowa City along with Keokuk and most of Washington county, was the only vulnerable Democratic seat to shift towards the Democrats in 2016. Trump did win the district, but by less than a point, doing 9 points worse than his statewide total. Johnson County was one of the few areas where Hillary improved over Obama’s 2012 performance, boosting Democratic fortunes in this district. This is likely the safest of the “vulnerable” democratic seats.

Table 5. Safe Democratic Seats and Competitive Measures

2014 State Senate Margin 2012 President Lean 2014 Secretary of State Lean Average Lean
Senate District 37 D unopposed D +17% D +17% D +17%
Senate District 21 D unopposed D +14% D +22% D +18%
Senate District 33 D +24% D +20% D +17% D +18%
Senate District 23 D +18% D +17% D +22% D +19%
Senate District 35 D unopposed D +24% D +20% D +22%
Senate District 45 D unopposed D +31% D +22% D +26%
Senate District 17 D +31% D +31% D +35% D +33%
Senate District 31 D unopposed D +35% D +32% D +34%
Senate District 43 D unopposed D +41% D +52% D +47%

The other 9 Democratic seats should be safe in the 2018 elections. They all lean at least 17 points towards the Democrats, and Republicans either didn’t bother to run candidates in 2014 or were blown out when they did field candidates in these seats. Given the pro-Republican tilt in the 2014 elections, it is hard to imagine them being competitive in 2018.


Overall, Republicans are vulnerable in 6 of their 11 seats, while Democrats are vulnerable in 5 of their 14 seats. As stated in the intro, the most likely outcome at this point seems to be a Democratic gain of a few seats, maybe 1 to 4 in total. Democrats are unlikely to achieve the clean sweep necessary to win back the majority, or even the 5 seat gain needed to achieve a tie, but it is certainly not impossible. If Democrats were to achieve that clean sweep, it would almost certainly be due to a large anti-Trump wave election, which would likely mean that Democrats had also won back the governor’s mansion and Iowa House. Obviously that would be a dramatic reversal of Democrat’s fortunes in Iowa after the disastrous 2016 elections, but more surprising things have happened.


by Nick Conway
Posted 1/4/18

CATEGORIES: Uncategorized


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