Support from independents is fueling an early advantage for Senator Casey in the Pennsylvania Senate race, even as big donors back his challenger, hedge fund manager David McCormick.

A new survey from Quinnipiac University found that Mr. Casey, who is a Democrat, enjoys an early lead over the expected Republican nominee, Mr. McCormick, leading him 53 percent to 43 percent.

The survey found that this lead was fueled by support from independents, who supported Mr. Casey ahead of Mr. McCormick, 55 percent to 39 percent. Mr. McCormick is not yet the GOP nominee. However, he is currently the only major candidate in the primary race.

“A big infusion of Indie support makes one of the most closely watched Senate races in 2024 a not-so-tight race,” Quinnipiac University polling analyst Tim Malloy said.

Mr. Casey also enjoyed more support from Republican respondents than Mr. McCormick enjoyed from Democrats, with Mr. Casey drawing support from 9 percent of Republicans and Mr. McCormick drawing support from 4 percent of Democrats.

As Mr. Casey enjoys the support of most independents, Mr. McCormick is enjoying the support of major figures on Wall Street, including Citadel chief executive Ken Griffin, Blackstone chief executive Stephen Schwarzman, and Elliott Management chief executive Paul Singer. Keystone Renewal confirmed to Bloomberg that the executives had been contributors.

A super PAC supporting Mr. McCormick, Keystone Renewal, announced that it had raised $18 million in the fourth quarter of 2023. In a statement, Mr. Griffin explained his support, saying that Mr. McCormick is a “proven business leader who understands what it takes to create jobs and grow a company.”

“This shows that there is not only real excitement and momentum for McCormick’s candidacy, but also the fact that Pennsylvania is a state that McCormick will win in November,” Keystone Renewal spokeswoman Brittany Yanik said in a statement.

Alongside the $6.4 million Mr. McCormick’s campaign raised in the final quarter of 2023 — including $1 million contributed by Mr. McCormick himself — the $18 million raised by Keystone Renewal will ensure that the effort to elect Mr. McCormick is well funded.

Mr. Griffin has previously been involved with Mr. McCormick’s election effort, hosting a fundraiser for Mr. McCormick alongside hedge fund manager Paul Tudor Jones and investing mogul Charles Schwab at Palm Beach in December.

The donations to Mr. McCormick from major donors comes in an era when competitive Senate races are becoming increasingly expensive.

According to the political spending watchdog, Open Secrets, the 2020 Georgia Senate races were the most expensive Senate races of all time, with more than $515 million spent in a race eventually won by Senator Warnock and more than $411 million being spent in the race won by Senator Osoff.

In 2022, the Senate race between Senator Fetterman and Dr. Mehmet Oz was the second most expensive that year, with more than $407 million dollars spent between the campaigns and outside groups. The only more expensive race that year was in Georgia.

Mr. Casey, for comparison, only raised about $3.6 million in the fourth quarter of 2024, with the vast majority — 92 percent — of the money coming from donations of less than $100, according to the campaign.

Having ended the third quarter of 2023 with $7.4 million in Mr. Casey’s campaign war chest, he has likely raised around $11 million for his re-election campaign, though detailed Federal Election Commission reports are not currently available.

“Pennsylvanians are rallying behind Senator Casey’s message to lower costs for families, stand up to China, and fight for workers because he’s delivering on them,” Mr. Casey’s campaign manager, Tiernan Donohue, said in a press release. “Now Pennsylvanians are sending Bob Casey into the election year with growing momentum and support that will carry him to re-election in one of the most competitive races in the country.”

The Cook Political Report currently rates the Senate race in Pennsylvania as “lean Democrat.”