Justice Sutherland's opinion in the Curtiss-Wright Case.[33]

The Youngstown Opinion appears to rest on the proposition that since
Congress could have ordered the seizure, e.g., under the necessary and
proper clause, the President, in making it on his own, usurped
"legislative power" and thereby violated the principle of the Separation
of Powers. In referring to this proposition, the Chief Justice (in his
dissenting opinion, for himself and Justices Reed and Minton) quoted as
follows from a 1915 brief of the then Solicitor General of the United
States on this same question:

The function of making laws is peculiar to Congress, and the
Executive can not exercise that function to any degree. But
this is not to say that all of the _subjects_ concerning which
laws might be made are perforce removed from the possibility
of Executive influence. The Executive may act upon things and
upon men in many relations which have not, though they might
have, been actually regulated by Congress.

In other words, just as there are fields which are peculiar to
Congress and fields which are peculiar to the Executive, so
there are fields which are common to both, in the sense that
the Executive may move within them until they shall have been
occupied by legislative action. These are not the fields of
legislative prerogative, but fields within which the lawmaking
power may enter and dominate whenever it chooses. This
situation results from the fact that the President is the
active agent, not of Congress, but of the Nation.[34]

Or, in more general terms, the fact that one of the three departments