If the Senate caves, and allows a fifth progressive Justice, the reaction of the grassroots Republicans will be something to behold. It is far from clear the Establishment understands quite how angry the conservative base already is, or how a cave-in on the Court would make this anger incandescent.
So the Senate leadership should hold the line. Yes, a divided Supreme Court is a bad thing, but the basic reason is that the four progressives see themselves as super legislators supporting the progressive movement. If they were less political, the Court could function with only eight, as it has at times in the past.
The Senators should not allow the progressives to use their own recalcitrance as a bludgeon, which is a variation of the old game “well, somebody around here has got to be reasonable, and it is not going to be me, so you must give in.” The Obama administration has run this game repeatedly, and the congressional leadership keeps falling for it. Stop. Scalia’s successor should be appointed by the next President.