The upcoming Senate elections in 2024 present a daunting challenge for Democrats, who will be defending more seats in politically volatile territories than in any other election of the 2020s. This includes the last three Senate seats held by Democrats in states that favored Donald Trump in 2020, and five more in states where President Joe Biden won by a slim margin of 3 percentage points or less.
Conversely, Republicans face no such challenge, as they are not defending any Senate seats in states that voted against Trump in 2020 or preferred him by a narrow margin of 3 points or less. This stark contrast underscores the high stakes for Democrats in improving Biden’s standing in key swing states by November.
Modern Senate elections have shown that it is increasingly difficult for candidates from either party to win seats in states that typically vote for the opposing party’s presidential candidate. Senate Democrats running in challenging electoral landscapes may defy this trend in the fall. However, if they fail, Biden’s performance in November could determine the control of the Senate not only in 2025 but for years to come.
A strong recovery by Biden, resulting in victories in most of the key swing states, could position Democrats to remain competitive in the battle for Senate control throughout the remainder of the decade, even if they narrowly lose the majority in November. However, if Biden loses most of the swing states, Democrats could face a Senate deficit too large to realistically overcome for years, given the party’s limited opportunities to flip seats currently held by the GOP.
“If the bottom were to drop out for Biden, Democrats could lose the Senate for a long time,” warns Kyle Kondik, managing editor of the political newsletter “Sabato’s Crystal Ball,” published by the University of Virginia’s Center for Politics. This prospect carries significant implications not only for the passage of legislation but also for the composition of the federal courts, particularly the Supreme Court.
Four of the Supreme Court justices will be older than 70 by 2028. Even if Biden retains the White House in 2024, a durable Republican Senate majority might refuse to fill any vacancies, echoing the actions of then-Majority Leader Mitch McConnell during Barack Obama’s presidency in 2016. “You can imagine Supreme Court seats going unfilled for years,” Kondik said.
The Senate in the 21st century has been characterized by small and fleeting majorities. In the 12 congressional sessions since 2001, one party or the other has reached 55 Senate seats only three times. By comparison, one party or the other won a majority of 55 or more Senate seats seven times in the 10 sessions from 1980 to 2000. Smaller majorities have proven more difficult to defend, resulting in control of the Senate flipping in the elections of 2002, 2006, 2014, and 2020.
The growing correlation between how states vote for president and how they vote for the Senate has limited the number of Senate seats each side can win absent unusual circumstances. This has resulted in a near-complete alignment between presidential and Senate outcomes. Heading into the 2024 election, Republicans hold 47 of the 50 Senate seats in the 25 states that voted for Trump in 2020. Democrats, in turn, hold 48 of the 50 Senate seats in the 25 states that voted for Biden.
However, this apparent balance masks a deeper divergence that largely explains the risk to Democrats this year. While Biden and Trump each won 25 states in 2020, Biden won many of them by very narrow margins. As a result, Senate Democrats are much more dependent than Republicans on states that lean their way only slightly in the presidential contest.
In 2020, Biden won three states by less than a single percentage point: Arizona, Georgia, and Wisconsin. He won three others by less than 3 percentage points: Pennsylvania, Nevada, and Michigan. Democrats now hold 11 of the 12 Senate seats from these six highly competitive states. By contrast, among the 25 states that backed Trump, North Carolina — where Republicans hold both Senate seats — was the only one Trump carried by less than 3 percentage points.
This contrast creates a huge disparity between the parties. Democrats now hold 14 inherently vulnerable Senate seats, while Republicans hold at most six. “When you have so many states where it is now inconceivable that they could go the other way, Democrats always have to get a straight flush,” said Michael Podhorzer, the former political director for the AFL-CIO. “They’ve got to run the table, because on the basis of what’s safe on either side in the Senate, or the Electoral College, they are at a huge disadvantage.”
This year, Democrats are defending five of their 11 seats in the states that Biden won by 3 points or less. This is the largest concentration of seats from those states that Democrats must defend in any single election this decade, from 2020 through 2028.
Democrats also face an unexpected challenge in Maryland — a state that leans much more reliably toward them in presidential elections — after GOP former Gov. Larry Hogan announced his run for the open seat there. In addition, Democrats must defend all three of their remaining Senate seats in the states that voted for Trump in 2020.
Both parties agree the open West Virginia seat is virtually guaranteed to flip to the GOP. Tester and Brown both have strong personal brands, but Biden is almost certain to lose their states, and possibly by substantial margins. If he does, Brown and Tester could survive only by breaking a nearly inviolate recent pattern in presidential election years.
In 2016, for the first time ever, every Senate race was won by the same party that carried the presidential contest in that state. In 2020, every Senate race again followed the presidential outcome — except in Maine, where Collins won reelection despite Biden’s victory there.
This pattern proved especially frustrating to Democrats, who raised enormous sums in 2020 for Senate candidates in Republican-leaning states such as Kentucky, South Carolina, Iowa, Kansas, Montana, and Texas. Yet when Trump comfortably carried those states in November, all of those Democratic Senate candidates lost as well.
This year, with West Virginia likely already gone, if either Brown or Tester loses, it would be very difficult for Democrats to maintain their Senate majority into 2025. The only Republican senators they might plausibly oust to offset those losses are Rick Scott in Florida and Ted Cruz in Texas. Democrats have recruited strong challengers to each of them, but both of those races clearly lean toward the GOP, especially in a presidential election year.
But if Democrats can hold down their Senate losses to some (or even all) of their three seats in the states Trump won in 2020, they would emerge with a deficit small enough to overcome in upcoming elections. The real long-term risk for the party this November is losing several of their Senate seats in the states Biden narrowly carried last time.
If Democrats lose Senate seats in the narrow Biden states, they simply have very few places on the map to replace them, given the parties’ patterns of support. It’s that prospect that has led the Democratic data analyst David Shor to warn for years that if the party doesn’t perform well in the 2024 presidential election, the GOP could seize control of the Senate for a sustained period.
“There is a real downside risk that if the presidential election goes poorly, the Republicans could not only win the Senate but build something of a cushion that would be hard for Democrats to cut into in the near future,” Kondik said. Gene Ulm, a Republican pollster who has worked for many Senate candidates, agrees that what happens in the narrow Biden 2020 states this fall will cast a huge shadow on control of the Senate through the decade.
Unless and until such a new political configuration emerges, both parties can realistically target many fewer Senate seats than they could even two decades ago. But the ceiling is clearly lower for Democrats than for Republicans. It leaves Democrats, even in good years, with achingly little margin for error to build a Senate majority. And unless Biden recovers more strength, 2024 may be very far from anything Democrats would call a good year.