Earlier this month, House Republicans provoked a constitutional showdown with President Obama over the debt ceiling, a confrontation in which Obama prevailed. Now Senate Republicans are provoking a different kind of showdown over judicial appointments. The proximate subject is the D.C. Circuit Court -- a kind of mini-Supreme Court with sweeping authority over national policy, and whose composition will help shape the fate of Obama's second term. But the constitutional question at stake looms larger still. The Senate has submitted another nominee, Patricia Millett, to one of the Court's vacancies. Republicans are filibustering again. The question is whether Democrats back down, change the rules to stop judicial filibusters, or the parties work out another compromise.