While Americans will be voting for president in 2024, millions of other voters across 34 states will also be choosing who will represent them in the US Senate. Democrats will be defending 23 (20 Democrats and three independents who caucus with Democrats) while Republicans are defending 11 seats of their own.
In a CNN analysis of the top 10 most competitive senate races next year, eight of the ten most likely to flip are currently held by Democrats, with Republicans only fighting to keep two closely contested seats. Democrats currently hold a slim 51-seat majority, meaning they can only afford one net loss in order to maintain control with Vice President Kamala Harris casting the tie-breaking vote. If Republicans win back the White House in 2024, a Republican vice president would break the tie in an evenly divided 50-50 US Senate.
CNN's rankings of the incumbent senators facing the closest reelection battles are listed below:
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1. Senator Joe Manchin, D-West Virginia
2. Senator Jon Tester, D-Montana
3. Senator Sherrod Brown, D-Ohio
4. Senator Bob Casey, D-Pennsylvania
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5. Senator Kyrsten Sinema, I-Arizona
6. Senator Jacky Rosen, D-Nevada
7. Senator Tammy Baldwin, D-Wisconsin
8. Senator Debbie Stabenow, D-Michigan (retiring)
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9. Senator Ted Cruz, R-Texas
10. Senator Rick Scott, R-Florida
Sen. Manchin's ranking at the top of the list is consistent with his position as a Democratic senator in a state that Donald Trump won in 2020 by nearly 40 percentage points. Manchin — along with Sen. Sinema — is responsible for tanking Democrats' hopes of passing President Joe Biden's Build Back Better Act in 2021. Manchin initially said he would accept a $4 trillion bill, before convincing his colleagues to scale back the public investment legislation to $2 trillion, before ultimately declaring it dead.
The swing state of Pennsylvania is typically seen as a must-win for both parties, as its electoral college votes have played a deciding role in the past two presidential elections. Pennsylvanians may ultimately also decide which party controls the US Senate, as they did in 2022 when Democrat John Fetterman narrowly defeated Republican Mehmet Oz and secured his party's majority. Bob Casey is a longtime, well-known incumbent running for his fourth term, though Republicans will likely pour millions of dollars into an effort to flip the seat.
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Kyrsten Sinema's reelection bid may also be one of the most hotly contested races of 2024, as she'll be in a three-way race with presumptive Republican nominee Kari Lake — who lost the Arizona gubernatorial election last year — and Rep. Ruben Gallego (D-Arizona), the likely Democratic nominee. Gallego entered the race in January of 2023, not long after Sinema officially left the Democratic Party to affiliate as an independent.
