Senate Democrats head into Tuesday’s election facing the fight of their lives: defending a 51-49 majority with a map so formidable that Republicans have called it their best opportunity in a decade to gain ground.

Republicans are already down nearly 50-50, with West Virginia Sen. Joe Manchin, an independent who is rallying with Democrats, pulling out, likely ensuring that GOP Gov. Jim Justice will replace him in one of the most intense states tomatoes from the country.

Now, Democrats have to basically run flush to hang on to the majority, leaning on a few entrenched incumbents and House members to keep red and purple state seats in their column as they pursue a set of extreme little to extremely difficult. return opportunities.

How to track ABC News has live coverage of the 2024 election results.

And even if they manage to hold all the blue seats, Democrats could still find themselves in the minority if former President Donald Trump defeats Vice President Kamala Harris, with VP nominee JD Vance serving as the GOP tiebreaker.

Here are five Senate races to watch on Tuesday that will help determine control of the Senate and how many races Democrats are on the hook for.

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Democratic Sen. Jon Tester, a three-term incumbent, has exited tough races before despite running in unfriendly territory. But his run for a fourth term may be his toughest challenge yet.

Tester is running against businessman and former Navy SEAL Tim Sheehy, a wealthy candidate who has been highly sought after by Senate GOP Leader Mitch McConnell and Sen. Steve Daines, the chairman of the Senate Republican campaign arm, who has the mission to dethrone Tester. his fellow Montanan.

The polls are disheartening for Tester — he’s behind by more than 5 points Polls average 538and he hasn’t driven in metrics since July 9.

Tester drew on his authenticity as a seven-finger farmer and third-generation Montanan to suggest he hears the concerns of his constituents and is fighting for them. He also hopes a ballot abortion referendum will help boost voter turnout among Democrats.

Meanwhile, Sheehy ran as a businessman who accuses Tester of being out of touch with the state’s increasingly Republican and generally dysfunctional Washington. He faced a series of attacks from Tester, including questions about how he got shot in the forearm and that he is not originally from Montana, a state that has long prioritized a sense of place but has seen increasingly many rich outsiders… staters buy land.

Still, Tester is believed to be facing tough odds despite his past success. Trump won the state by more than 16 points in 2020, and while Tester is expected to edge Harris, such a margin at the top of the ticket could be insurmountable for the incumbent senator.

Unless Democrats can pick up a GOP-held seat, a Tester loss would give Republicans the Senate majority.

Ohio

Democratic Sen. Sherrod Brown was also running for a fourth term in a state that flipped from purple to red, jeopardizing his re-election chances.

Brown is running as a blue-collar populist, with a gravelly voice and an often rumpled suit that highlights his everyman bona fides. A vocal union supporter and opponent of international trade deals before it was cool, Brown has consistently outbid the kind of white college-educated voters who used to vote Democratic but have defected en masse to Trump.

He also leaned heavily on the abortion issue after 57 percent of Ohioans supported a referendum last year protecting access to the procedure. He also ran ads with law enforcement endorsements as a way to separate himself from the Democrats’ national brand.

Brown faces Bernie Moreno, a Colombian immigrant and businessman. Moreno worked hard — and spent millions — to cast Brown as too liberal for a state that went for Trump by 8 points twice. He, too, has focused on social issues, including abortion and transgender athletes participating in women’s sports.

Moreno never drove in 538 poll averagebut he has cut Brown’s lead significantly, now trailing by just 1.2 points after dropping 6.5 points in late July. Moreno has been helped by a flurry of outside spending from Washington Republicans, who are looking to build as large a majority as possible, especially as Montana appears to be drifting further and further away from Democrats.

Here too, the presidential margin is expected to play a significant role. Like Tester, Brown is expected to run ahead of Harris. But if Trump widens his margin of victory a third time, Brown could face headwinds.

Michigan

The retirement of Democratic Sen. Debbie Stabenow has opened a prime opportunity for Republicans to fill a purple state vacancy.

The race pits Democratic Rep. Elissa Slotkin against former GOP Rep. Mike Rogers. Slotkin has a 3.5 point edge Polls average 538as well as a fundraising advantage, but the lack of an incumbent makes the race particularly palatable for Republicans.

Slotkin drew on her background as a CIA analyst who deployed to Iraq, Rogers’ votes against abortion protections and her cross-sectional appeal, including her endorsement from former Rep. Liz Cheney.

Rogers, meanwhile, embraced Trump after earlier criticism and attacked Slotkin over transgender athletes and concerns about making electric vehicles (Slotkin reiterates that he lives on a dirt road, but wants the “next generation” of vehicles to be manufactured in the state).

A massive X-factor in both the presidential and state Senate races is the war in Gaza, which has angered Michigan’s substantial Arab population and risks leaving voters disaffected and dissatisfied with President Joe Biden and the candidates Democrats this year.

Pennsylvania

Democratic Sen. Bob Casey, a three-term incumbent, is a fixture in Pennsylvania — his father was a former governor and the Casey name echoes throughout the state.

However, he will face a favored opponent in Dave McCormick, a former hedge fund executive who has been heavily recruited to run this year. He ran in 2022 but lost to Dr. Mehmet Oz in the GOP primary. Oz lost to now-Sen. John Fetterman, D.

Pennsylvania is home to fierce and competitive presidential races, and the Senate race is no different. Casey is up 2.6 points in 538 poll averagealthough this is down from a lead of over 8 points in August.

Casey and Democrats have attacked McCormick over abortion, his residence in Connecticut and past business ties to China. McCormick, meanwhile, embraced Trump after toppling him in 2022 after endorsing Oz, and accused Casey of being out of touch with Pennsylvania and not very rooted in Washington, pushing voters to “make a change” on Tuesday.

Arizona

Accord Sen. Kyrsten Sinema, an independent who caucuses with Democrats, announced in March that she would not seek a second term, creating a primary opportunity for Republicans.

However, Kari Lake, the failed gubernatorial nominee in 2022 and this year’s Senate nominee, is on the back foot.

Rep. Democrat Ruben Gallego held a steady lead in Polls average 538 even though Trump is believed to have an advantage in the state at the presidential level.

Race is a rare case of low name recognition being advantageous, especially in a state like Arizona that values ​​pragmatism.

Gallego has an extensive background as a progressive, but he hasn’t been a particularly well-known lawmaker outside his district, giving him a chance to recast himself as a moderate, including supporting things like increased border enforcement after hitting his border wall Trump.

Lake, meanwhile, became a MAGA rock star in 2022, especially after criticizing “McCain Republicans” and refusing to accept his loss in the gubernatorial race that year. She has sought to moderate this year, including reaching out to former Gov. Doug Ducey, but has a more established firebrand image than Gallego, making it difficult to appeal to centrists in and around Phoenix, who hold the key to victory in Arizona. .

She has yet to acknowledge the results of her 2022 race or Trump’s 2020 loss.

The race could provide key clues about how Democrats might keep Latino voters in their fold amid widespread concerns about defections this year. Gallego, of Colombian and Mexican descent and a combat veteran, said he has spoken to Latino voters who say they will support both him and Trump.

The race will also serve as a barometer of sorts in the Senate general. Republicans will rue a missed opportunity if Gallego wins, but if Lake can pull off a win, it likely means Republicans had a good night elsewhere, too.

Democrats’ offensive opportunities

Democrats are playing in a small handful of Republican-held seats, though they face strong odds of flipping any of them.

GOP Sens. Ted Cruz of Texas and Rick Scott of Florida face Rep. Colin Allred and former Rep. Debbie Mucarsel-Powell, respectively. FiveThirtyEight polling averages show both Democrats within striking distance, and the national party has begun spending money there, particularly in Texas. However, both red states are tough territory for Democrats to win, especially in a presidential year.

Independent Dan Osborn is also challenging GOP Sen. Deb Fischer in Nebraska. Osborn has insisted he won’t run for either party in the Senate, but Republicans have worked hard to paint him as a Democrat in centrist clothing. Polls point to a close race, but Osborn also faces headwinds in a heavily Republican-leaning state.