Presidential powers are not fixed but fluctuate depending upon their disjunction or conjunction with those of Congress. We may well begin by a somewhat over-simplified grouping of practical situations in which a President may doubt, or others may challenge, his powers, and by distinguishing roughly the legal consequences of this factor of relativity.
1. When the President acts pursuant to an express or implied authorization of Congress, his authority is at its maximum, for it includes all that he possesses in his own right plus all that Congress can delegate. [n2] In these circumstances,[p636] and in these only, may he be said (for what it may be worth) to personify the federal sovereignty. If his act is held unconstitutional under these circumstances, it usually means that the Federal Government, [p637] as an undivided whole, lacks power. A seizure executed by the President pursuant to an Act of Congress would be supported by the strongest of presumptions and the widest latitude of judicial interpretation, and the burden of persuasion would rest heavily upon any who might attack it.
2. When the President acts in absence of either a congressional grant or denial of authority, he can only rely upon his own independent powers, but there is a zone of twilight in which he and Congress may have concurrent authority, or in which its distribution is uncertain. Therefore, congressional inertia, indifference or quiescence may sometimes, at least, as a practical matter, enable, if not invite, measures on independent presidential responsibility. In this area, any actual test of power is likely to depend on the imperatives of events and contemporary imponderables, rather than on abstract theories of law. [n3]
3. When the President takes measures incompatible with the expressed or implied will of Congress, his power is at its lowest ebb, for then he can rely only upon his own constitutional powers minus any constitutional powers of Congress over the matter. Courts can sustain exclusive presidential control in such a case only by disabling [p638] the Congress from acting upon the subject.[n4] Presidential claim to a power at once so conclusive and preclusive must be scrutinized with caution, for what is at stake is the equilibrium established by our constitutional system.