SJB:
McConnell has figured he has an opportunity to break Trumps hold over the GOP so he will vote for impeachment and a shed load of Republicans will vote with him. Game over for Trump.
McConnell himself has nothing to lose. He's just been elected for another 6 years after which he will retire so the threat of losing his seat is not a problem. He's pushed the Supreme Court to the right with Trumps help and he'll be hoping to regain control of the senate when the next round of elections come up in 2 years time. And maybe another more moderate (compared to DT) Republican President in 4 years time.
So possibly a pretty successful end to a long career. First step though - make sure there is no Trump comeback.
Yep, it really is all down to McConnell's influence on which way the impeachment will go. I'm not popping any champagne just yet though.