cts, is plenary as to those objects, the power over
commerce with foreign nations and among the several States is vested in
Congress as absolutely as it would be in a single government having in
its constitution the same restrictions on the exercise of power as are
found in the Constitution of the United States." The power, therefore,
is not to be confined by state lines but acts upon its subject-matter
wherever it is to be found. "It may, of consequence, pass the
jurisdictional line of New York and act upon the very waters to which
the prohibition now under consideration applies." It is a power to be
exercised within the States and not merely at their frontiers.

But was it sufficient for Marshall merely to define the power of
Congress? Must not the power of the State also be considered? At least,
Ogden's attorneys had argued, the mere existence in Congress of the
power to regulate commerce among the States did not prevent New York
from exercising the same power, through legislation operating upon
subject matter within its own boundaries. No doubt, he concedes,
the States have the right to enact many kinds of laws which will
incidentally affect commerce among the States, such for instance as
quarantine and health laws, laws regulating bridges and ferries, and so
on; but this they do by virtue of their power of "internal police," not
by virtue of a "concurrent" power over commerce, foreign and interstate.
And, indeed, New York may have granted Fulton and Livingston their
monopoly in exercise of this power, in which case its validity would
depend upon its not conflicting with an Act of Congress regulating
commerce. For should such conflict exist, the State enactment, though
passed "in the exercise of its acknowledged sovereignty," must give
place in consequence of the supremacy conferred by the Constitution upon
all acts of Congress in pursuance of it, over all state laws whatsoever.

The opinion then proceeds to the consideration of the Act of Congress
relied upon by Gibbons. This, Ogden's attorneys contended, merely
conferred the American character upon vessels already possessed of the
right to engage in the coasting trade; Marshall, on the contrary, held
that it conferred the right itself, together with the auxiliary right of
navigating the waters of the United States; whence it followed that
New York was powerless to exclude Gibbons's vessels from the Hudson.
Incidentally Marshall indicated his opinion that Congress'