on pp. 819-820 od raines:
We have always insisted on strict compliance with this jurisdictional standing requirement. See, e. g., ibid. (under Article III, "federal courts may exercise power only 'in the last resort, and as a necessity''') (quoting Chicago & Grand Trunk R. Co. v. Wellman, 143 U. S. 339, 345 (1892)); Muskrat v. United States, 219 U. S. 346, 356 (1911) ("[F]rom its earliest history this [C]ourt has consistently declined to exercise any powers other than those which are strictly judicial in their nature"). And our standing inquiry has been especially rigorous when reaching the merits of the dispute would force us to decide whether an action taken by one
of the other two branches of the Federal Government was unconstitutional. See, e. g., Bender, supra, at 542; Valley Forge, supra, at 473-474. As we said in Allen, supra, at 752, "the law of Art. III standing is built on a single basic idea-the idea of separation of powers." In the light of this overriding and time-honored concern about keeping the Judiciary's power within its proper constitutional sphere,3 we must put aside the natural urge to proceed directly to the merits of this important dispute and to "settle" it for the sake of convenience and efficiency. Instead, we must carefully inquire as to whether appellees have met their burden of establishing that their claimed injury is personal, particularized, concrete, and otherwise judicially cognizable.