The 2024 United States Senate election in Pennsylvania was held on November 5, 2024, to elect a member of the United States Senate to represent the state of Pennsylvania. Incumbent Democratic Senator Bob Casey Jr. lost re-election to a fourth term, being defeated by Republican nominee Dave McCormick in what was considered a major upset. Most predictions gave Casey a slight advantage, and he led in most polls. Along with Sherrod Brown in Ohio and Jon Tester in Montana, Casey was one of three incumbent senators to lose re-election in 2024, all of whom were Democrats first elected in 2006.
The primary election took place on April 23, 2024. The election was considered essential for Democrats' chances to retain their majority in 2024. The Associated Press and Fox News declared McCormick the winner on November 7, while Decision Desk HQ called the race for McCormick on November 14. CNN, NBC, ABC, and CBS all called the race for McCormick on November 21; Casey conceded the race later that day, halted a recount and confirmed the result.
This was Pennsylvania's closest US Senate election since the passage of the Seventeenth Amendment, as well as the closest Senate election of the 2024 cycle. McCormick was the only Republican challenger to win in a state flipped by Trump in the 2024 presidential election. The other three Republican Senate gains were in states Trump had won in all three of his runs. With Democrats flipping the other Senate seat two years earlier, this was the first time since the 2012 Senate election in Indiana where the opposite party flipped a seat after losing one in the previous cycle.
Notably, the margin of just 0.22% between the Republican and Democratic candidates is fewer than the votes received by either the Libertarian candidate, John Thomas (1.29% of the vote), the Green candidate, Leila Hazou (0.95% of the vote), or the Constitution candidate, Marty Selker (0.34% of the vote). This was Casey's first general election loss of his political career, and the second counting Casey's primary election loss in 2002. This election made Pennsylvania one of several states to have a younger senior senator (John Fetterman) and an older junior senator (McCormick). McCormick was sworn in on January 3, 2025.
Pennsylvania is considered to be a purple state at the federal level, especially since in the 2020 presidential election, Joe Biden carried Pennsylvania by about 1.2 percentage points. Democrats had controlled both U.S. Senate seats, the governorship, a majority of its U.S. House delegation, and the Pennsylvania House of Representatives. The last time Republicans won a U.S. Senate seat in Pennsylvania was in 2016.
Senator Bob Casey Jr. was first elected in the blue wave of 2006, defeating then-incumbent Senator Rick Santorum by about 17 percentage points. He was re-elected in 2012 by 9 percentage points (when he ran ahead of Obama by almost 4 points) and in the blue wave of 2018 by 13 percentage points. Given these three decisive victories, Casey's fourth term appeared inevitable for much of the race. However, tightening polls in the final weeks indicated a closer contest, even as Casey was largely considered the favorite to win.
Aggregate polls<br />
Bob Casey Jr. vs. Doug Mastriano<br />
Counties that flipped from Democratic to Republican
McCormick won nine of 17 congressional districts, with the remaining eight going to Casey, including one that elected a Republican.
In Pennsylvania, a statewide recount is triggered under state law if the margin falls within 0.5% of the total vote. Preliminary results for the election reached this threshold on November 13, 2024, with McCormick at 48.9% leading Casey's 48.6%, as outstanding ballots continued to be counted across the state. Secretary of the Commonwealth Al Schmidt officially ordered the recount later that evening, with Casey declining to concede. The deadline for the counties to begin their recounts is on November 20, the third Wednesday after the election according to state law, however, counties can start their recounts as early as November 18, with all counties required to submit their results to the Department of State by noon on November 26 as the results must be reported by the Secretary of the Commonwealth by noon on November 27. Additionally, the counties must use different machines for the recount than were used on Election Day.
On Monday, November 18, following a series of challenges and disputes, the Pennsylvania Supreme Court directed all of the state's county election officials not to count certain mail-in ballots which arrived on time yet lacked a correct handwritten date on the return envelope.
The last instance of a statewide recount being held was for the 2022 Republican primary for Pennsylvania's Class 3 Senate seat, of which McCormick was also a candidate. Conversely to his stance in the 2024 general election, he unsuccessfully sued to have undated mail-in ballots counted. After completion of the recount he would concede to Mehmet Oz, with the final results expanding Oz's margin by 49 votes.
McCormick benefitted from the presence of former President Donald Trump on the ballot, who carried the state over Vice President Harris by just over 120,000 votes (for a margin of roughly 1.7%) in the concurrent presidential election. Indeed, McCormick cleared 60% in most counties in the stateâÂÂs less-populated interior and even 70% in many.
Unlike in Ohio and Montana, however, McCormick had to seek support beyond the Trump base as he was running in a swing state. Casey and Trump both won Bucks, Erie, and Monroe Counties. McCormick campaigned with Nikki Haley in the suburbs of Pittsburgh and Philadelphia, aiming to appeal to voters uneasy about Trump by positioning himself as a more establishment candidate. Casey aired ads in late October to highlight his votes with the Trump administration, while McCormick tied Casey to Harris, highlighting his votes with the Biden administration. However, both candidates received fewer votes than their respective partiesâ presidential candidate in the concurrent 2024 presidential election. Senator McCormick received about 144,000 fewer votes than President Trump, while Senator Casey received almost 39,000 fewer votes than Vice President Harris.
Partisan clients<br />
Official campaign websites