After the 2024 election, Democrats are at a steep disadvantage in the Senate

Much of the coverage of the outcome of the 2024 election has focused on how President-elect Donald Trump will wield executive power to pursue his political goals over the next four years. Trump, however, will not be alone in Washington: Voters elected Republican majorities in the U.S. House and Senate as well. The two chambers could help Trump levy taxes on imports, close the U.S. border and begin the deportation of millions of undocumented immigrants. And with 53 seats in the Senate, in particular, Republicans will be able to approve a long list of Trump's judicial nominees, approve (or withdraw from) any treaties and, of course, sign off on his Cabinet nominees.

The coming, sudden U-turn in the policy output of the U.S. government is a reminder that elections have serious consequences in the short term. But the impact of the 2024 election could be felt for years in another important way: It may have relegated Democrats to long-term minority status in the Senate. According to a new 538 analysis, barring significant changes in the party's coalition, it will be tough for them to win a majority in coming elections — and implausible, verging on impossible, to win the 60-seat majority needed to overcome a filibuster (assuming that parliamentary maneuver isn't abolished).

Political sorting has hurt Democrats in the Senate

For decades, Democratic candidates for Senate in many rural states performed far better than those states' presidential partisanship, enabling the party to win large majorities unattainable with blue states alone. West Virginia Sen. Joe Manchin, for example, beat his Republican challenger in 2018 by 3 percentage points despite Trump winning the state by 42 points in the 2016 presidential race and former Massachusetts Gov. Mitt Romney winning it by 27 points in 2012. And Montana Sen. Jon Tester won reelection by 4 points in each of 2012 and 2018 even as Romney was carrying the state by 14 points in 2012 and Trump was winning it by 20 points in 2016.

This year, however, Tester lost by 8 points, and — with Manchin's retirement — Democrats lost their West Virginia seat by a whopping 41 points. These losses followed similar defeats for Democrats in deep-red Indiana, Missouri and North Dakota in 2018, as well as in Arkansas, Louisiana and South Dakota in 2014 and across the South in the 2000s.

In retrospect, future analysts may see the 2024 election as the death knell for the Democratic Party's viability in rural America. The party's losses this year have resulted in a national Senate map that is almost completely dictated by presidential partisanship. On Jan. 3, 2025, when the newest class of senators is sworn in, the Democrats will hail from 25 states, the reddest of which is Arizona. The Grand Canyon State leans 4.0 points to the right of the nation as a whole, per a weighted average of the two most recent presidential election results* — which means we'd expect a Republican presidential candidate to win the state by 4.0 points in a perfectly tied national election. By contrast, the class of Democratic senators who took office after the 2018 election spanned states from R+41 West Virginia to D+32 Hawaii.

In total, just six states represented by Democratic senators come 2025 will be redder than the nation as a whole (Arizona, Georgia, Michigan, Nevada, Pennsylvania and Wisconsin). A decade ago it was 11. Republicans, meanwhile, will have been elected from 28 states, the bluest (and only blue state with a Republican senator) being Maine.

This asymmetry should scare Democrats about their future if they don't figure out how to win back voters in these currently red, rural states. They hold plenty of seats that could be easy to lose. Today there are only 19 states that vote more Democratic than the rest of the country in presidential elections — those as or more blue than New Hampshire — while 31 are Republican-leaning. That means that, in a Senate that is strictly determined by presidential partisanship, Democrats would have only 38 seats, while Republicans would control a supermajority of 62 — more than enough to pass their agenda and overcome filibusters.

A bias toward small, rural states

It is not destiny for Democrats to be at a disadvantage in the Senate. Simply put, the chamber currently favors Republicans because Republican candidates generally do better among rural voters, and because small states and large states have equal representation in the Senate. If you sort states by population density,** in 2024 the most urban state (New York) voted for Vice President Kamala Harris over Trump by a margin of 12 points. The most rural, Wyoming, went for Trump by 46. Population density and Democratic margin were moderately correlated (r = 0.59) — meaning population density alone predicted about 35 percent of all variation in state-level presidential results this year.

But it wasn't always like this: As recently as the 1996 presidential election, there was rather little urban-rural polarization in state vote totals. Then-President Bill Clinton lost to Republican former Sen. Bob Dole in the most rural state by just 13 points, and the correlation between population density and presidential results was weaker, at 0.49 (which accounts for about 24 percent of the variance in results that year).

And because there are more small states than big ones, the party that is stronger with rural voters tends to enjoy an advantage from the way Senate seats are distributed (two per state regardless of population). Today, that party is the Republicans. One statistic to measure the size of their current advantage in the Senate is the difference between the presidential partisanship of the median state (which is also the median Senate seat) and the national popular vote.

If you put every state in order from reddest to bluest based on the same weighted average of the 2024 and 2020 presidential election results, the two states in the middle are North Carolina and Arizona, which are 2.7 points and 4.0 points more Republican than the nation as a whole, respectively. The average of these two numbers — the hypothetical median Senate seat — is R+3.4.

But this statistic actually masks the severity of the problem for Democrats. That's because it is subject to noise in the national popular vote, which can fluctuate because of changes in voting behavior in solidly red or blue states that don't actually affect a party's chances of winning competitive Senate seats. If you repeated the 2024 election, for example, and dropped turnout in deep-blue New York by 20 percent, then Trump would have won the popular vote by even more and the median Senate seat would appear less biased toward Republicans as a result.

The metric is also based exclusively on presidential results, which means it doesn't account for the possibility that a party's Senate candidates outperform its presidential candidates — as had been the case for the Democrats until recently. The party's real problem is not Democratic presidential candidates doing worse in Montana or West Virginia; they have been doing poorly there for a while. Their real problem is the loss of Senate candidates and incumbents who were able to shed the national party label and compete in places that are unfriendly to Democrats. As the Democratic Party brand has become more uniform across the nation, their expected Senate seat total has declined in close elections.

Incumbent losses hit Democrats especially hard

What we really need is a number that directly measures how well Democrats need to do in each cycle for their Senate candidates to win a majority, after taking into account how well Senate candidates have tended to perform in certain states. For this, we fitted a model to predict how each state would vote in each cycle in a hypothetical world in which every Senate seat is up for election every two years. (In reality, only about one-third of the Senate is elected every two years.)

To train this model, I began by splitting the Senate into 10 separate six-year periods from 2000 to 2024 (2000-06, 2002-08, 2004-10, etc.); since only a third of the chamber is elected every cycle, we need to include six years of results to capture the dynamics of each body of senators more accurately. When I fitted this model after the 2024 election, for example, I included all Senate elections held in 2020, 2022 and 2024. Then, I fitted a linear regression model to predict the Democratic margin in concurrent contested Senate races over the whole time frame based on the state and cycle in question, controlling for the candidates running for each party. Next, I used that model to predict the results of hypothetical Senate elections in each state simultaneously held immediately after the model's training period — say, if all states held Senate elections in 2026, subtracting the effects of incumbency for senators who lost their seat.

I then adjusted these predictions by adding additional votes for Democratic candidates uniformly in each seat until the party would hypothetically win 51 total seats in the Senate. Once I figured out what that number was each cycle, I computed the implied national popular vote margin for the chamber based on the adjusted forecasts for each state. The table below displays that margin alongside our original, presidential-only bias metric:

We can see now how bad the trend is for Democrats. While, at their best, they could have won the Senate while losing a hypothetical Senate popular vote in 2008, our model suggests the party would have needed to win nationally by 4.2 points in 2024 in order to be favored to win 51 Senate seats. For context, that's 5.7 points better than they did in the presidential popular vote. Moreover, if we run the 2024 election again but remove Democrats' incumbency advantages in the states where they lost seats (Montana, Pennsylvania, Ohio and West Virginia), while adjusting the value of incumbency in places they held (such as Arizona, where Democrat Ruben Gallego beat Trump's margin in the state by nearly 8 percentage points) — the template for the Democrats going forward — our model indicates they'd need to win the national popular vote by 6.1 points in order to be favored to win 51 seats.

As we can see, the benefit incumbency confers onto candidates is especially important to Democrats. This is because they hold Senate seats in those six states that currently lean to the right of the nation as a whole. Without incumbents in those seats, and assuming a neutral political environment, Democrats would be expected to lose six more Senate seats. Worse, losing those incumbents hits Democrats harder than it would hit Republicans to lose theirs, since Democrats rely more on Trump voters crossing over to support them in order to win seats.

Of course, long-term trends are hard to forecast, and this exercise is best suited for short-term analysis. Maybe by 2034 Democrats will have improved materially in, say, Texas, North Carolina and Georgia such that their disadvantage has disappeared. But what the party really needs is to figure out how its candidates in deep-red states can distance themselves from the national Democratic Party brand — or to change the national brand altogether. Without that, it will be hard for the party to win enough Senate seats to confirm (or block) judges and Cabinet nominees and effect major legislative change for the foreseeable future.

Footnotes

*Specifically, an average of the state's lean relative to the nation that gives 75 percent weight to the 2024 election result and 25 percent weight to the 2020 election result.

**I calculated each state's population density by first dividing the number of people living in each county in the state by the county's area in square miles. Then, I took the natural logarithm of that number. Finally, I calculated the average of each state's county population density weighted by the number of people living in each county.