Republican Rep. Lou Barletta raised just under $500,000 for his race against incumbent Sen. Bob Casey during the final three months of 2017, an amount concerning to Pennsylvania Republicans who worry the party is blowing an opportunity to oust a vulnerable Democrat.

Barletta, personally recruited to run by President Trump, spent nearly as much as he raised during the fourth fundraising quarter, to close the year with just under $1.1 million in the bank — far less than Casey's $8.6 million.

That could prove decisive in an election cycle shaping up as a backlash against Trump, even though he defeated Democrat Hillary Clinton in Pennsylvania in 2016, become the first Republican in decades to win the state's electoral votes. Barletta described his fundraising as making good progress after declaring for the race at the end of August.

"Our campaign has built great momentum heading into 2018," the congressman said in a statement. "The response we have received in a short time has been inspiring. We are well-positioned to take our message directly to the voters of Pennsylvania and defeat Bob Casey in November."

Barletta faces minor opposition in the Republican primary. With Trump's endorsement, the state party establishment is lining up behind him, although there are pockets of resistance.