Since a year is supposedly a lifetime in politics, some senators face dramatically new challenges when they go before voters once every six years. Five senators are up for reelection in 2024 in states that have trended against their party compared with 2018. With such a closely divided Senate, each race is an important part of the fight for the majority.

Each cycle has a unique set of circumstances, but Inside Elections’ Baseline and Vote Above Replacement (VAR) metrics are useful in analyzing what this class of senators is up against in this cycle.

Baseline captures a state’s political performance by combining all federal and state election results over the past four election cycles into a single score (a trimmed mean, to be specific). It seeks to approximate what share of the vote the “typical” Democrat or Republican might receive in any given state, showing significant trends that have emerged over the past few election cycles. VAR is simply the candidate’s share of the vote minus the party’s Baseline. A higher VAR indicates a strong performance relative to expectations, while a negative VAR is evidence of underperformance.

Here’s a look at key states with 2024 Senate races and the senators in those seats now.

West Virginia

Sen. Joe Manchin III is probably the only Democrat who could win a statewide election in West Virginia anymore, and even that might be a stretch for the incumbent. With six statewide wins going back to his 2000 election as secretary of state, Manchin could be perceived as being unbeatable. But his most recent election was not overwhelming, and the state has shifted significantly since he was last on the ballot. 

Despite the impeccable electoral record, Manchin was reelected in 2018 by just 3 points and with less than 50 percent of the vote against a flawed opponent, state Attorney General Patrick Morrisey. Manchin’s performance equated to a good-but-not-great VAR of 4.2, which means he won a little more than 4 percent more of the vote than a typical statewide Democrat in West Virginia at the time. While that was good enough to win in 2018, it won’t be in 2024, should Manchin choose to run again. 

After the 2018 elections, the Democratic Baseline in West Virginia was 45.4 percent. But that Baseline dropped to 37.6 percent following the 2022 elections. If Manchin overperforms by the same amount in 2024 as he did in 2018, he’d fall short of 42 percent and likely lose reelection.

In order to win, he’d need to post a VAR of closer to 12. No senator in a competitive race has scored higher than a 10 VAR in the past three cycles. In 2020, West Virginia’s other senator, Republican Shelley Moore Capito, earned an 11.5 VAR in a race that was never serious. 

Ohio

Democrat Sherrod Brown had the best VAR (9.4) in 2018 of any senator up for reelection in 2024, and he’ll have to overperform again to win another term. In 2022, Democrats saw just how difficult it’s become to win statewide in Ohio. Democratic Rep. Tim Ryan received national praise for his campaign but in the end lost by 6 points to a flawed Republican, J.D. Vance. Ryan’s VAR was 3 in 2022.

The somewhat good news for Brown is that the overall Baseline in Ohio hasn’t shifted dramatically over the past six years. It’s gone from a 9.6-point Republican advantage (53.6-44.1 percent) to an 11.2-point edge for the GOP (54.9-43.7 percent). So Brown will likely have to post a VAR of closer to 6 in order to win another term. And the senator probably won’t enjoy the 2-to-1 spending advantage he had last time. 

Montana

Compared with Ohio, Montana has shifted more dramatically to the right since Democratic Sen. Jon Tester last won reelection. On one hand, 2018 was a good cycle for Tester, as he won by 3.5 points over Republican Matt Rosendale and crossed the 50 percent threshold for the first time in his Senate career.

On the other hand, Republicans have grown their Baseline advantage in Montana by 5 points since 2018. Republicans have a 54.2-42.5 percent edge after the 2022 elections, compared with a narrower 51.7-45.2 advantage in 2018. That means if Tester overperforms a typical Democratic candidate by the same margin in 2024 as he did in 2018, he’d be short of 48 percent, and short of his winning percentages in 2006 and 2012. 

It’s certainly not impossible for Tester to do even better than his 5.2 VAR in 2018, but the best-performing Democratic senators in competitive races in 2022 were New Hampshire Sen. Maggie Hassan (4.1 VAR), Georgia Sen. Raphael Warnock (4.1 VAR), Colorado Sen. Michael Bennet (3.0) and Arizona Sen. Mark Kelly (2.8). That shows how difficult it is to overcome partisan trends in the current environment.

Pennsylvania

Democratic Sen. Bob Casey isn’t as vulnerable as some of his colleagues, but the Keystone State has shifted from Democratic-leaning to something closer to a swing state. After the 2018 elections, Democrats had a 6.6-point Baseline advantage (52-45.5 percent). That Democratic advantage has narrowed to 4.1 points (50.7-46.6 percent) following the 2022 elections, taking into account Joe Biden’s narrow victory in 2020. That gives Casey some breathing room, and he might need it. 

Casey won reelection easily in 2018 by 13 points over GOP Rep. Lou Barletta, 56-43 percent. But because of Democrats’ Baseline advantage, that was only a 3.7-point VAR for the senator. That same overperformance would be enough to win in 2024, but Casey could face a stronger, better-funded challenger this time around. Joe Biden’s narrow win in 2020 and Democrat John Fetterman’s 5-point win over a flawed challenger in 2022 show that Casey will likely have a serious race this cycle.

Texas

In 2018, GOP Sen. Ted Cruz won one of the highest-profile Senate races in the country, even though he underperformed in the process. His 50.9-48.3 percent victory over Democratic Rep. Beto O’Rourke translated into a -4.7-point VAR. That underperformance was worse than some of 2022’s most underwhelming GOP nominees, including Don Bolduc (-2.9), Herschel Walker (-3.1) and Blake Masters (-3.9).

The good news for Cruz is that Texas is not shifting left as fast as the narrative, even though it is less Republican. A 14.5-point Baseline advantage for Republicans after the 2018 elections has narrowed to a 10.8-point GOP Baseline advantage after the 2022 elections. That means Cruz could underperform by the same amount in 2024 and still win, albeit with less than 50 percent.

Nathan L. Gonzales is an elections analyst with CQ Roll Call.