I suspect the Grimes people have paid him off in an effort to cause her to win. mitch’s kamikaze action seem like like he's taking a dive.
“Reid says to me, he says ‘Kid, this ain't your election. We're going for the price on Grimes.’
I coulda been a contender. I coulda been somebody, instead of a bum, which is what I am, let's face it”
~future quote by Mitch the night of the next election
I think McConnell sees his mission now is to keep another conservative from getting elected, so to that end, he MUST BEAT BEVIN! If he loses in November, so be it, but at least it would be to a democrat, which is the natural order of things.
These people hate and resent the conservatives for taking out first Arlen Specter, then Bob Bennett, then preventing Mike Castle and Charlie Crist from becoming nominees and thus senators, then making Lisa Murkowski fight for her political life, then taking out Richard Lugar and then defeating David Dewhurst.
These old guard types literally HATE conservatives and will do whatever it takes to defeat them.
The base will return the favor and take Mitch's cushy sinecure away from him.