Bunning no doubt took special delight in endorsing Paul on Wednesday. With a clear jab aimed at McConnell, Bunning said Paul "will be his own man in Washington, not beholden to the special interests and beltway insiders who come looking for handouts on a daily basis."
I doubt Bunning's endorsement will make a real difference in the race, mainly because I think, with such a strong lead, Paul is already on track to win, but it does give Paul the appearance of having some support from Kentucky's Republican establishment. Bunning, at least for the Republican primary, could also potentially serve as a good surrogate for Paul at events or fund raising functions.
McConnell is not going to have Bunning to kick around anymore, but it looks like he might need to deal with Rand Paul in his caucus, whose possible election would be a result of him defying McConnell in his home state.