WASHINGTON — U.S. Rep. Lou Barletta, the leading Republican vying to challenge Sen. Bob Casey (D., Pa.), raised $1.26 million for his campaign fund in the first three months of the year, he announced Monday. The total marked a significant increase over his previous fund-raising, which had drawn some criticism for being too weak.

Barletta ended March with $1.63 million in his political war chest, his campaign said. That compares to slightly more than $10 million for Casey, who is seeking a third term and has been targeted by national Republicans in a state that President Trump won.

Barletta raised Republican concerns when he raised less than $500,000 in the previous reporting period — a relatively small sum for a challenger who holds public office and is running in a top-tier race. His latest figures are more in line with what might be required in such a contest. National donors and political groups often look to fund-raising figures as a sign of candidates' strength when they decide where to spend money and campaign resources, and Barletta is hoping for a major push from such groups to help overcome Casey's financial advantage.

"This was our biggest fundraising quarter yet, and we are excited by the momentum that is building behind Lou's campaign," his campaign manager, Cody Jones, said in a statement.

Barletta, a former mayor of Hazleton, is in his fourth term in the House but has never been a prolific fund-raiser and has never had to contend with competing in a statewide race.

His latest figures come a little more than a month ahead of the May 15 primary. State Rep. Jim Christiana is also seeking the Republican nomination.