It's easy to understand why many in D.C. assume that control of the House and Senate will change hands in 2024. First, there's the math. Senate Democrats, who have a one-seat majority, are defending 23 seats, including three in states Donald Trump easily carried. House Republicans are trying to hold onto their slim five-seat majority while protecting 18 incumbents sitting in districts carried by Joe Biden, including five districts Biden won by double digits.

Then there's the fact that churn and change have become commonplace, especially on the House side. When I first came to D.C. in the early 1990s, Democrats had been in the majority for more than 30 years. No House Republicans had ever been in the majority and no Democrats had been in the minority. Today, almost every member (but for those elected since 2022) have served in both the majority and minority. From 1954 until 2005 (51 years), control of the House changed one time. In the last 16 years, House control has flipped four times.

But, we also know that the political landscape will change between now and November of next year. Besides the obvious factors — like the state of the economy or an escalation of tensions with China — here are three other key factors that will determine control of Congress next year.

History

(The Senate version): If you define history as the last two presidential cycles, Republicans are in the driver's seat in 2024. Since 2016, only one Senate candidate, Republican Sen. Susan Collins, won in a state the presidential nominee of their party lost. If (recent) history repeats, Democrats would likely lose at least three seats — West Virginia, Montana and Ohio.

If your version of history extends to 2012, Democrats have a path to holding their majority. That year, six candidates (five Democrats and one Republican), won in states that the presidential nominee of their party did not. It also happens that two of those Democratic "overachievers" — Senators Joe Manchin and Jon Tester — are on the ballot this time around. Today, the question is whether Manchin (should he run for re-election), Tester as well as Ohio Sen. Sherrod Brown (whose state has since gone red) have the right combination of skill, luck and connection with voters to overcome the gravitational pull of polarization.  

(House version). As my colleague David Wasserman has noted, the House hasn't flipped in a presidential cycle since 1952 and hasn't flipped to the party occupying the White House since 1948, when Harry Truman barnstormed against a Republican "do nothing Congress." This has been the case even when the number of seats needed to flip was as small as it is this cycle. In 2000, Democrats needed just five seats to gain the majority in the House. They ended up gaining just one. 

Turnout Turn-around 

One reason the House has only changed hands in midterm years is that lower turnout midterms tend to benefit the "out party," while turnout in a presidential cycle is more evenly balanced. However, four straight cycles of higher-than-normal turnout and a more polarized electorate than ever have led to more unpredictable outcomes in the House. In 2020, Democrats were expected to pick up seats, but instead lost 12 and came within 30,000 votes of losing their majority. In 2022, Republicans underperformed expectations, winning their narrow majority by just 6,000 votes.  

One way to look at the outcome of 2022 is to say that but for Democratic "underperformance" in dark blue states like California, Oregon and California, Democrats would have held the House. According to Wasserman's calculations, House candidates in New York underperformed Biden's 2020 margins on average by 13 points. In California and Oregon, Democratic House candidates underperformed Biden by 7.6 points. 

Today, in New York and California alone, there are 11 GOP-held districts that Biden carried in 2020. Of those 11, five are districts Biden carried by double digits. In 2024, the thinking goes, "drop off" Democratic voters will return and, voila, there's an 11-seat gain right there. 

But, alas, it's not that simple. The most existential threat to House Democrats is redistricting. As my colleague David Wasserman has expertly documented, Republican redraws in North Carolina and Ohio could put at least three to four Democrats in serious danger. 

Another factor to consider is Democrats' "overperformance" in 2022's battleground states like Michigan and Ohio where abortion and weak GOP candidates helped juice Democratic turnout and dampen GOP enthusiasm. 

In Michigan, for example, Democratic Rep. Elissa Slotkin outperformed Biden's margin in her Lansing-based district by five points. Democrat Dan Kildee won his 8th CD by 10 points, an eight-point improvement over Biden's margin in that CD in 2020. In the Grand Rapids-based 3rd CD, Hillary Scholten outran Biden's margin by five points. 

In Ohio, Emilia Sykes won her Akron-based district by six points, a three-point improvement over Biden's showing in that CD in 2020. 

What happens when/if those less-than-enthusiastic Republican-leaning voters show up in 2024?

In 2020, for example, Pew's verified voter survey found that 13 percent of the overall electorate that year had not voted in 2018. Those "midterm drop-off" voters ultimately supported Trump by 8 points. 

The Republican Party has become more reliant on non-college white (and increasingly non-white non-college) voters. Those voters, however, are also the most likely to show up to vote only in presidential elections.  

Intra-party Headaches

(GOP version): My colleagues David Wasserman and Jessica Taylor recently wrote about the challenges Republican leaders face in getting their preferred candidates through contentious primaries. On the Senate side, Taylor highlights five states — West Virginia, Arizona, Pennsylvania, Ohio and Montana — where potentially complicated primaries could hurt Republican chances of taking back the Senate if a divisive, less broadly-acceptable nominee emerges. 

Wasserman looked at five GOP incumbents who are likely to face serious primary opposition from more MAGA-aligned challengers. While none of those five races should be competitive in a general election, "that doesn't mean, however, that primary contests won't have an impact on House control. If, for example, Republicans nominate more MAGA-oriented folks in swing/competitive districts like they did in 2022 (WA-03, OH-09), they could give Democrats more opportunities for victories."

(Democratic version): Sen. Krysten Sinema's decision to switch from Democrat to independent may have saved *her* a primary, but it's given Democrats a huge headache. First, and foremost the DSCC and other Democratic allies will have to decide whether to support the official Democratic nominee (likely Rep. Ruben Gallego), or their Senate colleague who, while identifying as an independent, still caucuses with Senate Democrats. 

Then there's the question of what a three-way contest between Sinema, Gallego and a GOP nominee would look like. Recent polling in the state showing Gallego leading in a number of potential scenarios is a bit misleading. After all, unlike his potential challengers (Sinema and failed GOP gubernatorial nominee Kari Lake), Gallego hasn't been hit with millions of dollars of negative advertising. The five-term congressman represents an overwhelmingly Democratic district and has never received less than 75% of the vote. Moreover, it's likely that Gallego will be attacked not just from Republicans, but from Sinema as well. A messy GOP primary only adds to the uncertainty of how this thing plays out in the fall. And the BIden campaign can't afford a "Democrats in disarray" scenario in this must-win state either. Overall, it's just a big mess.

On the House side, there were fewer instances on the Democratic side than the Republican side of extreme or weak candidates defeating the stronger, more ideologically-aligned candidate in 2022. Even so, Democrats would likely be short just four seats instead of five had Democratic Rep. Kurt Schrader not lost his primary to a more progressive Democrat. 

Competitive open seats to watch on the Democratic side include CA-47, where Democratic Rep. Katie Porter is retiring to run for Senate, and MI-07, where Rep. Elissa Slotkin is also running for Senate. 


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