Thanks to a SuperPAC, McCormick leads Casey in fundraising. For now.

Republican Senate candidate Dave McCormick’s billionaire-backed super PAC keeps banking money at a speedy clip. But incumbent Democratic Sen. Bob Casey’s campaign is raising steadily and will likely see more outside help as the race heats up.

By far the largest pot of money currently available in Pennsylvania’s marquee U.S. Senate race, one of the most hotly contested in the nation, is controlled by Keystone Renewal, a SuperPAC that last fall came out of the gate with $18 million in contributions from large-dollar donors. Those contributions were not subject to laws that limit what donors can give directly to political campaigns.

Based on filings made to the Federal Election Commission in the first quarter of this year, Keystone Renewal’s take is now up to $21 million. That money comes from just 41 donors, only two of whom live in Pennsylvania (Jeff Yass of Bala Cynwyd and Joseph Wesley of Newtown).

And so far, they’ve spent only $3 million of it.

In the fourth quarter of last year, the Casey campaign saw itself out-raised by a factor of two by newly announced challenger McCormick. Both campaigns’ takings were dwarfed by what Keystone Renewal brought to bear.

The pace of new funds brought in this quarter was far less lopsided. Both campaigns raised more than $5 million, with Casey pulling in slightly more. But donors also Keystone Renewal another $3.5 million: much less than in the previous quarter, but more than enough to widen the gap between the Democratic- and Republican-aligned war chests.

That leaves a formidable difference between what both sides can bring to the table in the coming months. While both campaigns have already spent roughly half of what they’ve brought in, Keystone Renewal has spent little so far.

Combined with the money that McCormick’s campaign has on hand, that leaves Republicans with access to nearly $25 million. Casey has less than half of that.

This is not to say that national Democrats are asleep at the wheel. Defending Casey’s seat will be essential to maintaining Democrats’ razor-thin majority in the U.S. Senate, which is threatened by retirements and changing electorates in states like Montana and Ohio.

To date, the Senate Majority PAC, an Democratic-aligned advocacy group, has pledged a whopping $42 million for ads supporting Casey, a number that would dwarf even what Keystone Renewal can muster. In addition, the Democratic Senatorial Campaign Committee, the fundraising arm of Democrats in the U.S. Senate, has pledged another $8 million.

That would put this year’s contest well on its way to challenging Pennsylvania’s 2022 race as the most expensive in history.

Staff writer Julia Terruso contributed to this article.