U.S. House average margins of victory were closest since at least 2012

By

Ballotpedia staff

Welcome to the Tuesday, Feb. 4, 2025, Brew. 

By: Lara Bonatesta

Here’s what’s in store for you as you start your day:

  1. U.S. House average margins of victory were closest since at least 2012
  2. President Donald Trump ends January with 48% approval, 45% disapproval
  3. Mike Zimmer wins Iowa Senate special election on Jan. 28

U.S. House average margins of victory were closest since at least 2012 

It’s been just over a month since the 119th Congress convened on Jan. 3, and as our lawmakers navigate things like the budget reconciliation process, cabinet confirmation hearings, and other business, we’re continuing our analysis of the 2024 election results with a review of congressional margins of victory. 

In the Jan. 30 edition of the Daily Brew, we took an early look at this data and zoomed in on the 80 congressional elections that were decided by 10 percentage points or fewer. Today, we’re expanding our focus to examine all 468 Senate and House elections that happened on Nov. 5 and their margins of victory.

An electoral margin of victory (MOV) is the difference between the share of votes cast for the winning candidate and the second-place candidate in an election. Margins of victory can be used to measure electoral competitiveness, political party or candidate strength, and, indirectly, the popularity of a particular policy or set of policies.

To kick things off, let’s check out some key numbers about the 33 Senate elections that happened in 2024.

The average MOV across all Senate elections in 2024 was 16.9 percentage points. That’s the second-narrowest MOV since we started collecting this data in 2012. The narrowest average MOV happened in 2018, when it was 16.8 percentage points. The average MOV for Democrats—including the two independents who caucus with them—who won U.S. Senate elections in 2024 was 14.4 percentage points. For Republicans, the average MOV in the 2024 U.S. Senate elections was 20.2 percentage points.

Let’s look at some noteworthy Senate races:

  • Elissa Slotkin (D) defeated Mike Rogers (R) in the open Michigan Senate race by 0.34 percentage points (48.6% to 48.3%). This was the narrowest MOV for a Democrat running for the Senate in 2024.
  • Incumbent Sen. Mazie Hirono (D) defeated Bob McDermott (R) in the Hawaii Senate race by 32.71 percentage points (64.6% to 31.9%). This was the largest MOV for a Senate Democrat in 2024.
  • Dave McCormick (R) defeated incumbent Sen. Bob Casey (D) in the Pennsylvania Senate race by 0.22 percentage points (48.8% to 48.6%). This was the narrowest MOV for a Republican running for the Senate in 2024.  On Nov. 13, Secretary of the Commonwealth Al Schmidt (R) announced that the result triggered a legally required statewide recount. The Department of State called off the recount after Casey conceded to McCormick on Nov. 21. 
  • Incumbent Sen. John Barrasso (R) defeated Scott Morrow (D) in the Wyoming Senate race by 50.99 percentage points (75.1% to 24.1%). This was the widest MOV for a Republican running for the Senate in 2024.

Three candidates–McCormick, Tim Sheehy (R-Mont.), and Bernie Moreno (R-Ohio)–defeated incumbents in their respective Senate races. The average MOV for those races was 3.7 percentage points.

Now let’s turn our attention to the House, where all 435 districts were up for election this year. The figures below exclude the 20 candidates—nine Democrats and 11 Republicans—who ran unopposed.

The average MOV across all House elections in 2024 was 27.3 percentage points. That’s the narrowest margin of MOV since we started collecting this data in 2012. The average MOV was 26.8  percentage points for the 206 Democrats who won their races and 27.9 percentage points for Republicans.

Let’s look at some noteworthy House races:

Biggest MOV changes from 2022 to 2024: (Excludes uncontested races, races without major party competition, and races where both candidates had the same party affiliation in either 2022 or 2024)

Eleven candidates–seven Democrats and four Republicans–defeated House incumbents. The average MOV for those races was 2.1 percentage points.

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President Donald Trump ends January with 48% approval, 45% disapproval

President Donald Trump (R) is now just over two weeks into his second term, and at the end of January, polling averages show him with a 48% approval rating. Forty-five percent of voters disapprove of his performance. 

Congressional approval is at 27%, and disapproval is at 48%. 

At this time during Trump’s first term in office his approval rating was 44% and congressional approval was 18%. At this point during the Biden administration, Biden’s approval rating was 53%, and congressional approval was 28%. Click here to see our comparison of opinion polling during the Trump and Biden administrations.

Ballotpedia’s polling index takes the average of polls conducted over the last 30 days to calculate presidential and congressional approval ratings. We average the results and show all polling results side-by-side because we believe that paints a clearer picture of public opinion than any individual poll can provide. The data is updated daily as new polling results are published.

Click on the provided links to see our polling index for presidential approval ratings and our polling index for congressional approval ratings.

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Mike Zimmer wins Iowa Senate special election on Jan. 28

ICYMI, let’s look back at a seat flip from a special election last week. On Jan. 28, Mike Zimmer (D) defeated Katie Whittington (R) in the special election for Iowa Senate District 35, 51.7% to 48.1%.

In November 2024, Gov. Kim Reynolds (R) appointed the previous incumbent, Sen. Chris Cournoyer (R), lieutenant governor, creating a vacancy in the 35th district. In 2022, Cournoyer defeated Jed Ganzer (D) 61% to 39%. 

In the 2024 presidential and congressional elections, President Donald Trump (R) won the district by 21 percentage points, and Rep. Mariannette Miller-Meeks (R) won by nine percentage points.

According to the Secretary of State’s office, Republicans have an edge regarding party registration in the district. At the time of the election, the 35th district had 12,246 registered Democrats, 15,598 Republicans, and 372 minor party voters. Additionally, 19,390 voters were registered as having no party affiliation. Voters cast 9,304 ballots in the special election. By comparison, voters cast 24,266 ballots in the 2022 general election.

Republicans maintain a two-thirds majority in both legislative chambers. 

Since 2010, 122 state legislative seats have switched partisan control in special elections. The chart below shows the number of changes by partisan affiliation between 2010 and 2025.

In 2024, all 100 seats in the Iowa House of Representatives and 25 seats in the Iowa Senate were up for election. As a result of the 2024 general elections, Republicans increased their majority in both chambers. The Republican majority in the House increased from 64-36 to 67-33. The Republican majority in the Senate increased from 33-16 with one vacancy to 34-16 with one vacancy. Following Zimmer’s victory, Republicans now have a 34-17 majority.

The Iowa General Assembly is one of 28 state legislatures where one party had a supermajority in both chambers. According to the Des Moines Register’s Stephen Gruber-Miller, this is the largest Republican majority in both chambers since 1970.

Iowa is also one of 23 states with a Republican trifecta. Republicans gained a trifecta in the state after gaining control of the Senate following the 2016 general elections.

This election is one of five legislative special elections that have taken place so far this year and one of 27 that have been called.

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