Michigan Sen. Gary Peters has signed on for another term as chairman of the Democratic Senatorial Campaign Committee, and he’ll face yet another challenging fight to hold the majority. But unlike in 2022, the 2024 battlefield looks historically lopsided against Democrats. 

Peters helped Democrats grow their Senate majority in 2022 in the face of a midterm environment made especially challenging by President Joe Biden’s mediocre job approval rating. Democrats couldn’t afford to lose a seat on a battlefield that included states that Biden won narrowly in 2020.

This cycle, the Senate battlefield is challenging in a different way. 

Democrats are defending eight vulnerable seats, while Republicans don’t have any. It’s the first time in at least 28 years that one party doesn’t have at least one vulnerable seat on the initial Senate battlefield. 

Eight Democrat-held seats are considered vulnerable, according to Inside Elections’ initial ratings. That includes three states that President Donald Trump carried in 2020 (Montana, Ohio and West Virginia), four states that Biden carried narrowly (Michigan, Nevada, Pennsylvania and Wisconsin) and Virginia, which Biden won by a more comfortable margin but looks potentially competitive after Glenn Youngkin’s gubernatorial win in 2021. 

Meanwhile, no Republican senators are up for reelection in states that Biden won. Looking at the initial 2024 Senate map, the most vulnerable Republican incumbent appears to be Rick Scott of Florida. But Florida is no longer a battleground state after GOP Gov. Ron DeSantis and GOP Sen. Marco Rubio were just reelected by close to 20 points.

It’s the first time in recent memory that one party doesn’t have a single vulnerable Senate seat on the initial battlefield. In initial ratings from Inside Elections and The Rothenberg Political Report going back to the 1994 cycle (when the Rothenberg Report started releasing formal ratings), each party has had at least two vulnerable seats. The battlefield includes any seats not rated as Solid Republican or Solid Democratic.

The closest recent comparison is probably 2014, when Democrats defended nine seats rated as initially vulnerable: Alaska, Arkansas, Louisiana, Massachusetts, Montana, New Hampshire, North Carolina, South Dakota and West Virginia. Republicans had two vulnerable seats (Kentucky and Maine), although they were rated as Likely Republican, on the outer ring of the battlefield. 

That discrepancy was one factor in a difficult cycle for Democrats as Republicans gained nine Senate seats. This cycle, Republicans need a net gain of two seats for a majority, or they can control the Senate by gaining one seat and winning the White House. 

Early in the 2016 cycle, Republicans were defending 10 vulnerable seats (Arizona, Florida, Georgia, Illinois, Iowa, New Hampshire, North Carolina, Ohio, Pennsylvania and Wisconsin).

Just Colorado and Nevada looked vulnerable on the Democratic side. Democrats gained two Senate seats that cycle.

Overall, 20 Democrats (and two independents who caucus with Democrats) are up for reelection in 2024, compared with just 11 Republicans and newly independent Sen. Kyrsten Sinema of Arizona. It’s Class I, for any congressional nerds keeping track at home, plus Republican Pete Ricketts, who was just appointed to Ben Sasse’s seat in Nebraska. 

This class used to be disproportionately Republican after the GOP gained eight seats in the 1994 wave. But the partisan makeup of the class started to shift six years later, when Democrats gained four seats. They gained six more seats (and the majority) in President George W. Bush’s second midterm election. Democrats gained another two seats in this class in 2012, when President Barack Obama won reelection. Republicans gained back two seats in this class in 2018 during Trump’s midterm election, but the disparity remains.

The overall size of the initial 2024 Senate battlefield is also small. It’s a total of nine seats, including Sinema’s seat in Arizona. Only two cycles in the past 28 years had smaller initial battlefields. There were just eight initially competitive races in 2022 and seven seats back in 2008. Over the past 20 years, the initial Senate battlefield has contained a dozen seats, on average.

Despite the challenging environment, Peters and the Democrats prevailed in 2022. So it’s premature to count them out in 2024 in the face of a uniquely difficult battlefield. But holding onto the Senate again will be tough, and it probably depends on the outcome of the presidential race at the top of the ballot.