HARRISBURG — Democratic Sen. Bob Casey raised more than $4 million in the last three months — his best fundraising quarter ever — as he awaits a Republican challenger to his reelection bid in the critical battleground state of Pennsylvania, his campaign said Wednesday.

Casey's campaign said the fundraising result beat the previous best quarter of his career by more than $1.2 million.

The campaign is reporting nearly $6 million in its bank account. That cash could prove crucial in ensuring Casey has the resources to successfully navigate a campaign in one of the nation’s most politically competitive states.

The second-quarter haul is giving Casey’s campaign some optimism that Democrats still enjoy support in the state following John Fetterman’s 5-percentage-point victory in last year’s race for Pennsylvania’s open Senate seat.

Casey, 63, is gearing up to seek his fourth term in office. He is a key ally of labor unions and President Joe Biden and gives Democrats a strong candidate in their defense of a seat in what is otherwise expected to be a difficult 2024 campaign to keep their 51-49 Senate majority.

Fetterman, who was Pennsylvania's lieutenant governor, also reported raising $4 million in his first quarter as a Senate candidate in 2021. Fetterman eclipsed that with a $22.4 million third quarter in 2022 on his way to beating Republican Dr. Mehmet Oz, who was endorsed by former President Donald Trump. Last year's Senate race was Pennsylvania's most expensive ever, at $420 million total, according to OpenSecrets, a Washington-based nonprofit organization that tracks campaign finance and lobbying data.

Casey comes into the 2024 race with strong name recognition — his father was a two-term Pennsylvania governor — and Republicans do not have a deep pool of potential recruits.

One Republican who may run is former hedge fund CEO David McCormick, who narrowly lost a bruising and expensive GOP nomination for the Senate in 2022 to Oz.

McCormick has said he is “seriously considering” running. He brings deep pockets and connections across the worlds of government, finance and Republican politics following a career on Wall Street and at the highest levels of President George W. Bush's administration.

But many Republicans acknowledge that it will be difficult — or impossible — to beat Casey.

In Pennsylvania, Casey has run statewide seven times already, winning six of those races, and has never run a close race for the Senate. He won his 2018 race by 13 percentage points and kept an active schedule on the campaign trail last year by helping Fetterman.