Democrats face an uphill battle to keep the Senate majority on the difficult electoral map US elections 2024

Thirty-four U.S. Senate seats — a third of the 100-member chamber — are up for grabs Tuesday in contests that could influence the makeup of the new government, the balance of the Supreme Court and policies on everything from foreign policy to abortion.

Democrats are trying to hold on to a one-seat majority, knowing the odds look slim given the impending retirement of West Virginia Sen. Joe Manchin and the likelihood that his seat will almost certainly go to a Republican seem.

Elsewhere, the party faces tough battles, with incumbents trying to hold on to 23 seats, often in states that are increasingly Republican-leaning as Donald Trump has increased his influence over the party.

In contrast, only 11 Republican senators are up for re-election, all in states where Republicans are well represented, leaving Democrats significantly less room for gains.

The most vulnerable incumbent Democrat is widely considered to be three-term Montana Sen. Jon Tester, who, if polls are accurate, is likely to face defeat against a Republican challenger, Tim Sheehy, a former Navy Seal who is supported by Trump.

A victory for Sheehy, whose campaign has faced allegations that he made racist comments about the state's indigenous community, could alone be enough to put the Senate in Republican hands – unless Democrats manage to get a Republican one to remove incumbents elsewhere.

However, Tester is not the party's only weak point.

Also at risk is Sherrod Brown, whose Ohio seat is rated a flop by the Cook Political Report in the face of a challenge from Bernie Moreno, a former car dealer and immigrant from Colombia who has also aligned himself with Trump.

About $500 million was poured into advertising spending, making it the most expensive Senate race in history. Brown has sought to emphasize shared policy goals with Trump — including support for anti-fentanyl legislation — in a once-fought state that the Republican presidential nominee is expected to easily hold.

The tactic could be successful as recent polls show Brown, at 71, narrowly ahead.

Also crucial are the races in the three Democratic “blue wall” states, Pennsylvania, Wisconsin and Michigan, whose proximity reflects the tough presidential contest between Kamala Harris and Donald Trump.

In Pennsylvania, Democratic incumbent Bob Casey – a senator for 18 years – is seeking a fourth term against a challenge from Republican Dave McCormick. McCormick, who funded his own campaign, has tried to link Casey to the same policies that Trump attacked Harris over, namely immigration and past support for a fracking ban.

The race was called a neck-and-neck by the Cook Political Report, as was the race in Wisconsin between another incumbent Democrat, two-term Sen. Tammy Baldwin, and her Republican challenger Eric Hovde, a wealthy banker and real estate developer who is a another self-finances the campaign.

Democrats are also on the defensive in Michigan, where House member Elissa Slotkin is running for the seat left vacant by the resignation of her Democratic colleague Debbie Stabenow. Her Republican opponent is Mike Rogers, a former Republican House member and former FBI agent who was once a critic of Trump but has now won his support.

Another weak point for the Democrats is Nevada, where the party's incumbent senator, Jacky Rosen, is in a tough race with Sam Brown, a decorated Army veteran who was seriously wounded in Afghanistan. Brown has tried to deflect Rosen's attacks on his abortion stance, saying he would not support a nationwide ban and admitting that his wife had once undergone the procedure.

In Arizona, Ruben Gallego, a U.S. Marine Corps veteran, is trying to retain a Democratic seat after independent Sen. Kyrsten Sinema, who voted with the party in the House, retired. Facing him is Kari Lake, a Trump ally who baselessly claimed that her failed bid for the state's governorship in 2022 was doomed by Democratic fraud.

Given this promising situation for Republicans, Democrats have only a small number of potentially winnable Republican seats in which to pull off an upset.

Chief among them is Texas, where outspoken 2016 Republican presidential candidate Ted Cruz faces a well-funded challenge from Colin Allred, a former professional football player turned civil rights lawyer. Democrats hope Allred can take a step beyond Beto O'Rourke, who narrowly edged out Cruz in the 2018 Senate race, losing 2.6% of the vote.

Other hopeful, if less likely, Democratic hunting grounds include: Florida, where Republican Sen. Rick Scott is running against Debbie Mucarsel-Powell, a former House member; and Nebraska, where incumbent Republican Deb Fischer is being challenged by Dan Osborn, an independent labor leader.

In both the Texas and Nebraska elections, their pro-GOP strength was recently downgraded from “likely Republican” to “lean Republican” in the Cook Report.