Updated: 12:24 p.m.

Sen. Jim Bunning (R-Ky.), the Senate’s most vulnerable incumbent who recently described his fundraising as “lousy,— pulled in less than $263,000 in the first three months of the year.

According to Federal Election Commission reports available on Thursday, Bunning raised $262,980, spent $37,224 and had $375,747 in the bank at the end of March.

Bunning, who had just $150,000 on hand at the end of 2008, has blamed his poor fundraising totals on GOP leaders — including his fellow Kentuckian and Senate Minority Leader Mitch McConnell (R) — who he says are trying to force him to quit the race by discouraging donors to give to his campaign. Bunning is considered the most imperiled Republican Senator in 2010, and some party insiders admit that they don’t have confidence that he can hold the seat.

Bunning had less cash on hand than the $388,500 that Lt. Gov. Daniel Mongiardo (D), who entered the race in January, reported having in his coffers. Mongiardo raised $429,552 since throwing his hat into the race.

Mongiardo was quick to release a statement this morning calling Bunning’s poor fundraising totals an indication that “Kentuckians are tired of his arrogance and blind support of Republican policies which have put our economy at risk, resulting in higher unemployment, higher healthcare costs, higher college costs and placed retirement at risk for thousands of Kentucky seniors.—

Kentucky Attorney General Jack Conway (D) also announced plans to run earlier this month, but his first fundraising report isn’t due until the end of June.