The constitutional separation of powers is lubricated by the comity each branch owes to the other two. Comity encompasses due respect for the prerogatives and obligations of other branches. When shared powers are at play, the bare minimum that is required is reciprocal action within a reasonable amount of time. The Constitution defines the time limit for a President’s signature or veto of legislation presented to him from Congress and the consequences for his refusal to act within that time limit. No precise time limit exists for other joint actions, and that probably renders one branch’s inaction nonjusticiable. It does not follow, however, that there can be no constitutional violation for inaction in all such circumstances....