While some senators up for reelection in 2024 have seen the partisan ground shift away from them since 2018, a handful of incumbents get to run on more favorable terrain. With such a closely divided Senate, even subtle changes could matter in 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 major 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 five more key states with 2024 Senate races and the senators in those seats now. Michigan has trended slightly more Democratic since 2018, but since Democratic Sen. Debbie Stabenow is not running for reelection, it doesn’t qualify for this list.

Nevada

Democratic Sen. Jacky Rosen will likely face a serious challenge in 2024, but she’ll get to run on more favorable terrain compared to the last time she was on the ballot. A 2.4-point GOP Baseline advantage after the 2018 elections (48.2-45.9 percent) is now a 1.7-point Democratic Baseline advantage after the 2022 elections (48.6-46.8 percent). 

Even though Nevada is clearly a battleground state, taking into account Joe Biden’s narrow win in the 2020 presidential race, Democratic Sen. Catherine Cortez Masto’s close call in 2022 and Democratic Gov. Steve Sisolak’s loss last cycle, Rosen has got to like the overall trend. 

[These states’ partisan changes since 2018 could decide Senate control]

Rosen ran a strong race in 2018 against GOP Sen. Dean Heller. Her 4.6-point VAR was a bit better than Sen. Joe Manchin III’s 4.2, even though her Democratic colleague from West Virginia has a reputation as an electoral juggernaut. If Rosen can replicate something close to her overperformance in 2024, she’ll be in good shape for a second term. 

Wisconsin

Democratic Sen. Tammy Baldwin was supposed to be one of the most vulnerable incumbents in 2018, but her reelection race didn’t end up being particularly close. Baldwin’s strong performance included an 11-point win and a 6.5-point VAR, the best score by a Democratic senator that cycle except Ohio’s Sherrod Brown and Minnesota’s Amy Klobuchar.

The challenge for Baldwin is that she represents the most competitive state in the country, according to Baseline. The state has shifted slightly to the left over the past six years, to a 1-point Democratic edge (49.6-48.6 percent) after the 2022 elections from a razor-thin 0.1-point GOP edge (48.9-48.8 percent) after the 2018 elections. 

Even though Baldwin has proved to be a strong candidate, the nature of the state still points to a serious race in 2024. 

Florida

GOP Gov. Rick Scott knocked off Democratic Sen. Bill Nelson in 2018, but the race was decided by less than 1 point, and Scott underperformed a typical statewide Republican with his -1.4-point VAR. 

The good news for Scott is that Florida has shifted toward Republicans since the last time he was on the ballot. Republicans now have an 8.8-point Baseline advantage (53.9-45.1 percent) in the Sunshine State compared to 2018, when Republicans had a more narrow 4.5-point Baseline edge. 

The burden of proof is on Democrats to demonstrate they can seriously compete statewide in Florida right now. Huge reelection victories by GOP Gov. Ron DeSantis and GOP Sen. Marco Rubio last year must give any serious Democrats pause before jumping into this race against Scott. 

Virginia

Despite Republican Glenn Youngkin’s high-profile win for governor in 2021, Virginia has shifted to become slightly more Democratic since 2018. Democrats now have a 5.6-point edge (52.3-46.7 percent) compared to a 5.1-point advantage (51.6-46.5 percent) following the 2018 elections. 

That was the cycle in which Democrat Tim Kaine won a second term. GOP nominee Corey Stewart had problems consolidating the party after the primary and convincing national strategists it was a real race. Kaine earned a solid 5.4-point VAR, but the outcome of the race wasn’t ever really in doubt even though Virginia was still considered a battleground state. 

The parties are close enough that Virginia should still be considered a battleground, but Republicans have a tough road ahead based on Kaine’s most recent performance and the overall trend of the commonwealth. 

Arizona

Arizona is complicated. The Grand Canyon State has moved toward Democrats since 2018, although Republicans still have the edge. The GOP has just a 1.8-point Baseline edge now compared to 4.9-point advantage when this seat was up previously. Running as a Democrat, then-Rep. Kyrsten Sinema had a 3.3-point VAR in her win over Republican Sen. Martha McSally. 

But those figures don’t matter as much, considering that Sinema is now an independent. Her path to victory, should she choose to run for reelection, is complicated and doesn’t fit neatly into partisan categories. Right now she’s unpopular in Arizona, and her fate probably depends on the two parties nominating candidates outside of the mainstream. 

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