Mitch is calling for the vote on Friday because he knows that he doesn’t have the vote solid for Kavanaugh. And the longer he waits, the further the Kavanaugh story evolves, the fewer votes he will have.
He want to get it over with so that they can start with a replacement nominee and get him/her approved before the mid-terms.
A Friday vote is figuratively a throw of the towel into the ring.
“I take no responsibility at all.” Donald Trump
“Anyone who wants a test can get a test.” Donald Trump