FILE - This combination of images shows from left, Republican Pennsylvania Senate candidate David McCormick, left, in Pittsburgh, on Sept. 21, 2023, and opponent, Sen. Bob Casey, D-Pa., in Chicago, on Aug. 22, 2024. (AP Photo Gene J. Puskar, left; and AP Photo Paul Sancya, File)

PHILADELPHIA — Democratic incumbent Sen. Bob Casey Jr. faces a well-financed challenge from Republican Dave McCormick in Pennsylvania’s nationally watched U.S. Senate race.

While Casey held a lead for much of the campaign, the race tightened in the final days, with observers seeing it as a toss-up as voters head to the polls.

Casey, a mild-mannered centrist whose father was a Pennsylvania governor, is seeking a fourth six-year term. McCormick, a West Point graduate and Gulf War veteran, is a former hedge fund CEO who benefited from tens of millions in spending from a super PAC funded by finance industry billionaires.

While the race may not determine control of the Senate, given that Republicans are likely to pick up seats in West Virginia and Montana, it could play a major role in determining the strength of the GOP’s expected majority. If Casey and a handful of other Democratic incumbents survive, Republicans will have little margin for defections in the upper chamber over the next two years.

Tuesday marks McCormick’s second attempt to win a Senate seat in Pennsylvania. He lost narrowly in the 2022 GOP primary to Mehmet Oz, the celebrity physician who in turn was defeated by U.S. Sen. John Fetterman, D-Pa.

That year, former President Donald Trump endorsed Oz, which was seen as a snub to McCormick because his wife, former Goldman Sachs managing partner Dina Powell, served in Trump’s administration as a deputy national security adviser. In 2024, Trump endorsed McCormick, who faced no significant competition in the primary.

That set the stage for a race with no less on the line than in 2022, given the Senate’s narrow partisan margins, but with a significantly different tone than the matchup featuring the polarizing and headline-grabbing personalities of Oz and Fetterman.

Casey is a rank-and-file Democratic senator who preaches the virtues of bipartisan civility, while McCormick is a clean-cut Army man-turned-businessman. And while neither man shied from attacking the other on the campaign trail, there was little drama in the race, and voters were left with a relatively simple choice between a career politician and a plutocratic newcomer.

Throughout the race, McCormick faced questions about his ties to Pennsylvania. Even this year, it was reported that he repeatedly flew on private jets back to Connecticut, where one of his daughters from a previous marriage still lives.

Born in western Pennsylvania and raised in Bloomsburg, McCormick went to West Point and served in the Gulf War. He then spent about a decade in Pittsburgh, where he led the software company FreeMarkets, before joining the Bush administration in 2005.

After leaving Washington in 2009, McCormick became an executive at the Connecticut-based hedge fund Bridgewater Associates, meaning he hadn’t lived in the Keystone State for about 17 years before launching his political career around 2022.

A Scranton native, Casey followed his father’s footsteps into the political arena when he won a 1996 election to become state auditor general. Shortly after winning reelection, he launched a campaign for governor in 2002, falling short to the eventual winner, former Philadelphia Mayor Ed Rendell, in the only loss of Casey’s career.

He rebounded by winning a 2004 election to become state treasurer, and in 2006 made national headlines by unseating U.S. Sen. Rick Santorum, a high-profile conservative Republican.

Casey entered politics as a candidate in the mold of an old-school Pennsylvania Democrat, fiscally liberal and socially conservative. As a “pro-life Democrat,” he opposed marriage equality for same-sex couples and fought efforts to regulate guns. He has since changed his positions on all three of those issues to align with the national Democratic platform.

But he has retained a populist economic agenda, supporting organized labor, opposing efforts to restrict the natural gas industry, and fighting against free trade agreements, including ones proposed by Democratic presidents.

This year, Casey’s messaging on inflation — he calls it “greedflation” and blames it on profiteering corporations rather than government spending — has been embraced by Vice President Kamala Harris campaign and other Democrats.

Both campaigns expected a tight race despite Casey starting out with a significant polling lead due to Pennsylvania voters’ greater familiarity with him. Thanks in no small part to a months-long deluge of TV advertising, McCormick’s profile grew, and the contest was widely viewed as a toss-up in the final weeks.

The race saw more than $300 million in spending by the campaigns, their parties, and outside spending groups. The largest outside spender was Keystone Renewal, a pro-McCormick super PAC backed primarily by finance industry billionaires, some of whom knew the Republican from his days at Bridgewater.

The PAC’s spending was crucial to making McCormick financially competitive in just his second run for office against a man who had won statewide elections, including races for Pennsylvania auditor general and treasurer.

McCormick’s strategy for much of the race was to tie Casey to President Joe Biden and Harris’ agenda, which the Republican cast as radical and too liberal for Pennsylvania.

Casey, on the other hand, leaned in heavily to McCormick’s time at Bridgewater, highlighting the firm’s leading role in investing in China and two allegations that McCormick helped cover up unfair treatment of female employees.

Neither candidate criticized his respective party’s presidential nominee, but both sought to create some daylight between them and the top of the ticket.

Casey emphasized repeatedly that he does not support a ban on natural gas fracking, a position Harris took in 2019 but has since backed away from. And McCormick said throughout the race that he believed Biden won the 2020 presidential election, which is usually seen as an affront to Trump.