The issue of marriage is not enough for schism.  Any Cardinals who doubt the unity of the faith can keep talking like they have the option and they will find plenty of orthodoxy.  There is the larger question of whether the Church can adapt itself to a modern understanding of human sexuality.  My bet is that we will and the clergy will follow suit.  The laity is too advanced to not pull the rest of the Church into modernity.  Let's not confuse stubbornness with piety.  Treating people decently in matters sexual is not a sin, its a virtue.

Sessions will go as far as Trump lets him.  Obama and Holder decided to not counter local marijuana laws with federal authority.  That was entirely their discretion and can be undone with a memo.  That was always the danger in not changing federal law at the same time.  Of course, if Sessions provokes backlash, federal change may be the result, although possibly not for two years.  We will see with the neo-liberals do.  Like with Daniel Burke.