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Congress, his authority is at its maximum, for it includes all that he possesses in his own right
plus all that Congress can delegate. In these circumstances, 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 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.
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 the Congress from acting
upon the subject. 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. [Ibid. at 63538.]