Bunning is behind in fundraising, Politico reports. His most recent financial report, from September, said that he had $175,000 in his campaign account, while other Republicans facing 2010 campaigns have at least four times as much.
Senate Minority Leader Mitch McConnell, R-Ky., spent $21 million in his last campaign.
"They don't have the fundraising guns to understand how difficult a fundraising climate they're in," a Kentucky operative said of Bunning's political staff. "It's going to be a nightmare,"
Bunning himself shows no sign that he is ready to step down.
"It's a free country," he said in a statement. "Anybody can run for anything they choose. I am gearing up, and I look forward to the challenge of taking on whoever comes out of the Democrat primary in May of 2010."
Bunning, a Hall of Fame pitcher with the Tigers, Dodgers and Phillies, served in the House from 1987 to 1999. He won close races in 1998 and 2004 to the Senate.