Less than a week after Kentucky Sen. Jim Bunning (R) acknowledged that his first-quarter fundraising was going “lousy,— his Democratic challenger announced that he raised $420,000 in six weeks of campaigning.

Kentucky Lt. Gov. Daniel Mongiardo (D), who kicked off his fundraising efforts in mid-February, raised more in the first six weeks of campaigning than he raised in the first six months of his 2004 run against Bunning, which he went on to lose by just 2 points.

But Mongiardo isn’t expected to have a free ride to the Democratic nomination next year. State Attorney General Jack Conway (D) appears set to throw his hat into the race. And while Conway certainly has some powerful allies, the attorney general lost some momentum for his would-be bid in late March when Gov. Steve Beshear (D) announced his endorsement of Mongiardo.

Whoever emerges from the Democratic primary will likely face the Senator, who is widely considered the most vulnerable incumbent up for re-election this cycle.

His low fundraising numbers, erratic behavior and poor performance in early polls has fueled a sense of doubt in GOP circles that Bunning can win again in 2010.

In recent weeks, Bunning has lashed out at his own party’s leadership for his fundraising woes. Last week, Bunning claimed Senate Minority Leader Mitch McConnell (R-Ky.) and National Republican Senatorial Committee Chairman John Cornyn (Texas) are working to fuel doubts about his 2010 prospects in the minds of possible donors and actively working to undermine his campaign. Previously, Bunning has charged that Cornyn and McConnell have been working to recruit a primary challenger to run against him.

At the end of 2008, Bunning showed just $150,000 in his campaign account.