Sen. Jim Bunning (R-KY) has announced that he will not run for re-election in 2010, after months of speculation about what he would end up doing.

In most cases, an open seat is a blow against the party controlling it. But this time, Bunning may have done the GOP a favor. Previous polling had shown Bunning running much poorer against his Democratic challengers than Kentucky Sec. of State Trey Grayson, the likely Republican nominee now that Bunning is out. In both his 1998 and 2004 races, Bunning just barely defeated his Democratic opponents in a state that is usually much more friendly to Republicans at the federal level.

Bunning had previously made open accusations against his party's leadership, accusing them of trying to force him into retirement by undercutting his efforts to raise money. About three months ago, he gave a green light to Grayson to start raising money for the race, apparently a sign that he was anointing his successor.

On the Democratic side, there is currently a primary between Lt. Gov. Dan Mongiardo, who just barely lost to Bunning in 2004, and state Attorney General Jack Conway.

Late Update: In his official statement, Bunning again slams his party leadership for sabotaging him:

"Unfortunately, running for office is not just about the issues. To win a general election, a candidate has to be able to raise millions of dollars to get the message out to voters. Over the past year, some of the leaders of the Republican Party in the Senate have done everything in their power to dry up my fundraising. The simple fact is that I have not raised the funds necessary to run an effective campaign for the U.S. Senate. For this reason, I will not be a candidate for re-election in 2010."