For Senate Democrats, 2024 is the year of living dangerously.
In this fall’s Senate elections, Democrats will be defending more seats in precarious political terrain than in any other election during the 2020s. That list of challenging elections this year includes the final three Senate seats Democrats hold in states that voted for Donald Trump in 2020, and five more in states that President Joe Biden won by 3 percentage points or less. Meanwhile, Republicans this year are not defending any Senate seats in states that voted against Trump in 2020, or preferred him by 3 points or less.
That math underlines the stakes for Democrats in Biden improving his position in the key swing states by November. One of the most powerful trends of modern Senate elections is that it has become exceedingly difficult for candidates in either party to win seats in states that usually vote the other way for president.
The Senate Democrats running in difficult electoral terrain might break that trend this fall. Yet if they can’t, Biden’s fate in November could determine control of the Senate not only in 2025, but for years thereafter.
A strong recovery by Biden in which he wins most of the key swing states could position Democrats to remain competitive in the battle for Senate control through the remainder of this decade, even if they narrowly lose the majority in November. But if Biden loses most of the swing states, Democrats could fall into a Senate deficit too large to realistically overcome for years — especially because the party has so few plausible opportunities to flip seats now held by the GOP.
“If the bottom were to drop out for Biden, Democrats could lose the Senate for a long time,” said Kyle Kondik, managing editor of the political newsletter “Sabato’s Crystal Ball,” which is published by the University of Virginia’s Center for Politics.
That prospect has enormous implications not only for the passage of legislation but also for the composition of the federal courts, especially the Supreme Court. Four of the Supreme Court justices will be older than 70 by 2028. Even if Biden holds the White House in 2024, and a vacancy arises, a durable Republican Senate majority might refuse to fill any of those seats — just as then-Majority Leader Mitch McConnell did while Barack Obama was president in 2016. “You can imagine Supreme Court seats going unfilled for years,” Kondik said.
The default position for the Senate in the 21st century has been for 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, not surprisingly, have proved more difficult to defend: In this century, control of the Senate has already flipped in the elections of 2002, 2006, 2014 and 2020.
The principal reason the chamber has become so closely divided is the growing correlation between how states vote for president and how they vote for the Senate. That has limited the number of Senate seats each side can win absent unusual circumstances.
Through the late 20th century, it was common for voters to split their tickets by electing senators from one party while voting for the presidential nominee of the other. After the 1984 election, for instance, Democrats still held about half the Senate seats in the states that voted for Ronald Reagan in both of his winning presidential campaigns.
But now the alignment between presidential and Senate outcomes has become nearly complete. 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 last time.
This surface equivalence in the two parties’ position in the Senate, though, 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 far more 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 those six highly competitive states. (Ron Johnson of Wisconsin is the only Republican senator from these 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. Even extending the net to states Trump won by less than 5 percentage points brings in only Florida, where Republicans also hold both Senate seats.
This contrast creates a huge disparity between the parties. Democrats now hold 14 inherently vulnerable Senate seats: their three from the states Trump won in 2020, and their 11 in the states Biden won only narrowly. For Republicans the total is at most six: two in states that Biden won in 2020, and four in states that Trump won narrowly, even with Florida included.
“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. That’s the biggest concentration of seats from those states Democrats must defend in any single election in this decade, from 2020 through 2028.
This year’s Senate races in the narrow Biden states include Democratic incumbents Bob Casey in Pennsylvania, Tammy Baldwin in Wisconsin, and Jacky Rosen in Nevada; also on the ballot is an open Democratic-held seat in Michigan (where the party is very likely to nominate Rep. Elissa Slotkin) and the Arizona seat held by Kyrsten Sinema, an independent who caucuses with Democrats. Sinema hasn’t indicated whether she will seek reelection, but Democratic Rep. Ruben Gallego is already running for the seat. (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 last week said he would run for the open seat there.)
In addition, Democrats this year must defend all three of their remaining Senate seats in the states that voted for Trump in 2020. That includes incumbents Jon Tester in Montana, Sherrod Brown in Ohio, and the open seat being vacated by the retiring Joe Manchin in West Virginia. Neither of the two remaining Senate Republicans in states that Biden won last time (Susan Collins in Maine and Johnson in Wisconsin) are up this year; nor are either of the GOP senators from North Carolina, the state Trump won by his smallest margin.
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. (Hogan’s bid in Maryland adds a wild card, but the probability that Biden wins Maryland will likely leave Hogan as an underdog despite his personal popularity.)
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.
Shor would not comment on the Democrats’ Senate situation, but many other analysts see a dangerous convergence: The party must defend an unusually large number of seats in terrain that is highly contested at the presidential level precisely as Biden is struggling in polls against Trump. “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. If Republicans capture Ohio, Montana and West Virginia, he said, the reaction in the political world would not be “gosh, shock, alert the media,” he said.
“It’s one thing for Republicans to recapture those states that have been habitually red,” Ulm said, but “if all of a sudden you have Republicans winning places that are historically purple,” that creates a very different situation going forward.
The best-case scenario for Democrats is that Biden recovers enough to win most or all of the five battleground states where the party is also defending Senate seats. Many on both sides agree that it will be difficult for Republicans to flip any of those Democratic-held seats if Biden wins the state — with Arizona a possible exception if Sinema creates a three-way race.
Of the Democrats running in the narrow Biden states, Casey in Pennsylvania and Baldwin in Wisconsin are probably best positioned to win even the president he loses their state, many in both parties agree. Brown and Tester also have deep roots that could allow them to survive Biden defeats as well. But in this era of greater party-line voting, it won’t be easy for any candidate to overcome such an undertow: Hardly any Senate Democrats in competitive races ran even 2 percentage points ahead of Biden’s vote share in 2020.
Ulm sees two keys to the Senate outcomes in the competitive swing states. One is the choices in the Senate races by voters who back third-party presidential candidates out of distaste for both Biden and Trump, assuming they face each other again; it is very difficult at this point, Ulm said, to predict how those disaffected voters will vote in Senate (and House) races.
For Ulm, the other key question is what happens with the voters who are slightly negative about Biden. He is confident Republican Senate candidates will romp among voters who strongly disapprove of Biden, as they did in 2022. But one reason Democrats blunted the anticipated 2022 red wave is their congressional and gubernatorial candidates ran unusually well among voters who only “somewhat disapproved” of Biden — largely because many of those voters considered the Trump-allied GOP alternatives too extreme.
That risk to the GOP remains. “The soft disapprovers are going to be a much more competitive constituency, just like 2022,” Ulm said.
David Bergstein, communications director for the Democratic Senatorial Campaign Committee, notes that in the 2022 midterm election, Democrats won Senate races in most of these same battleground states, although exit polls showed substantial discontent with the economy and Biden’s performance then, too. “Senate campaigns are candidate versus candidate battles,” Bergstein said. “We have the superior candidates, and Republicans are putting forward candidates who have big flaws, who lost races before, or are facing the prospect of damaging primaries. Certainly a presidential cycle is different than a midterm, but the laws of Senate campaigns, where candidate quality matters, are still in effect.”
Gary Jacobson, a professor emeritus of political science at the University of California at San Diego who specializes in Congress, said that given the fissures opening in each party’s coalition during the Trump era, no one should rule out the possibility that either side may develop new opportunities that reconfigure the Senate’s precarious balance.
“This structural disadvantage the Democrats have is a real thing and it will make it an uphill battle for them to control the Senate for the foreseeable future,” Jacobson said. “But the foreseeable future is pretty short. Political configurations are not cut in stone.”
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.