Kentucky is probably the best example of the monumental trouble the GOP is in this cycle. Mitch McConnell has been in the Senate since 1985 and won reelection in 2002 by about a forty billion votes. He's also the Senate Minority Leader. In other words, he should be cruising to victory.
Instead, McConnell is locked in a tough fight with Bruce Lunsford, who's not even a particularly accomplished politician. For that reason, it seems likely that McConnell will close the deal, but his weakness is a sign of larger forces at work.