How about a variation of #5? Maybe the Republicans fear they’ll win, and then the minority of Republican amnesty supporters won’t be able to join with Democrats to pass amnesty. Maybe they see this as a last chance, in their political careers, to do an amnesty cram down on the American people.
That's my suspicion. The liberal repubs want the Dems to share the blame on this, so both groups can play the old finger-pointing game. They don't want to go it alone and their window of opportunity is sliding closed.