The problem is that Schumer is not a Clintonista. Sure he's a liberal democrat. Sure, he owes Hillary! big-time. But he has ambitions of his own. His first loyalty will always be to Chuck Schumer. He wants to be a senior respected Senator, or maybe more, and he can't do that with Hillary! stealing all his face time. I mean, nobody gets between Chuckie and a TV camera without getting knocked down flat. Nobody except Hillary!, that is.
So Chuckie has to go, to be replaced with a Clintonista-to-be-named-later. Chuckie is just not reliable enough. And then there is this business about Hillary! being the Junior Senator from New York. That has got to wrankle. Senior Senator from New York just sounds so much better.