Schumer announced last week that Democrats would filibuster Gorsuch’s confirmation, which is a remarkably stupid decision. Since he was nominated in replacement of Scalia, Gorsuch wouldn’t fundamentally change the ideological balance of the Supreme Court. This means that, if Schumer has enough votes to deny Gorsuch a cloture vote that would send his confirmation to the floor, Republicans in Senate will be under intense pressure to go nuclear and get rid of the filibuster, because their base would never accept that they let the Democrats get away with denying Trump a nomination that would not even affect the ideological composition of the Court. Thus, if Schumer manages to get the votes he needs to carry out his threat and it comes to this, McConnell will go nuclear.
If he does, the Democrats will have no way of blocking a potential nomination later in Trump’s term that would change the ideological balance of the Supreme Court, which could happen if Kennedy or Ginsburg died/retired by 2020. On the other hand, if the filibuster were preserved, they could at least hope that some Republicans would refuse to get rid of the filibuster to confirm someone who would fundamentally alter the ideological composition of the Court. Furthermore, many Republicans in Senate are not hardcore conservatives, so they would probably balk at going to war with the Democrats to replace Kennedy, let alone Ginsburg, with someone like Pryor. But they couldn’t refuse to do so unless they had some kind of excuse, which is precisely what the filibuster would give them, because otherwise their base would skewer them.
Of course, Schumer knows that, but he and the other Democrats in Senate are under intense pressure from their base to systematically oppose Trump. Activists don’t understand that, in the case of Gorsuch’s confirmation, this would only harm their cause. Indeed, the debate about Gorsuch’s nomination is a textbook example of a party being screwed by its base, a pretty common phenomenon. If you try to explain that to liberals, they invariably start rambling about Garland, which is completely irrelevant. You can’t be successful in politics if you ignore basic political realities and the reality is that Republicans have a majority in Senate whereas the Democrats didn’t when Obama nominated Garland. (Moreover, given the map that Democrats face in 2018, this is unlikely to change any time soon.)