[Pearls Before Swine]

Schumer doesn't even hold a majority leadership position in his house of Congress.

Yes, but he controls enough votes to block through filibuster. And, it is his judgement that McConnell won't go nuclear and eliminated it entirely (although he certainly will, given the future opportunity).

[Alberta's Child]

If the Republicans had 50 votes in the Senate to end this shutdown, McConnell would pass it through a reconciliation bill.

McConnell is holding fast on the 60-vote requirement because he knows he doesn't even have 50 votes.