Constitution of the United States, Article I, Section 8 (the "Commerce Clause", in pertinent part)
The Congress shall have Power To lay and collect Taxes, Duties,
Imposts and Excises, to pay the Debts and provide for the common
Defence and general Welfare of the United States; but all Duties,
Imposts and Excises shall be uniform throughout the United States;
To borrow Money on the credit of the United States;
To regulate Commerce with foreign Nations, and among the several
States, and with the Indian Tribes;
explicitly grants Congress the power to "regulate Commerce with foreign Nations".
Article II, Section 1 of the Constitution of the United States
The executive Power shall be vested in a President of the United
States of America
explicitly grants the President "executive Power", which in addition to the Office having the power granted by Article II, Section 2
The President shall be Commander in Chief of the Army and Navy of the United States
grants the Office "implied" powers (see U.S. Foreign Policy Powers: Congress and the President by Jonathan Masters, Council on Foreign Relations, March 2, 2017) to act directly in foreign policy. Congress can and previously has granted the President authority to act relevant to the foreign policy objectives of the United States. The Executive also has the power to issue an Executive Order.
Separation of powers (see The Federalist Papers : No. 47 The Particular Structure of the New Government and the
Distribution of Power Among Its Different Parts
From the New York Packet. Friday, February 1, 1788. Madison) is designed to be flexible; with the Supreme Court of the United States
being the arbiter of the of powers granted to the two adjacent wings of the single trilateral body politic, if a controversy as to the exercise of those enumerated powers arises under the Constitution of the United States (see Political Questions in International Trade: Judicial
Review of Section 301? by Erwin P. Eichmann and Gary N. Horlick, Michigan Journal of International Law, Volume 10, Issue 3, 1989).
The answer to the question depends on agreement between the Legislative Branch and Executive Branch as to what the foreign policy objective is; and which Branch of Government is asked the question, whether that be before or after the fact of Executive action.
The Supreme Court of the United States is the only Branch (Judicial) of Government which is explicitly granted power by the Constitution of the United States to resolve a case or controversy as to the rights of the parties arising under the Constitution and Laws of the United States, at Article III, Section 2
The judicial Power shall extend to all Cases, in Law and Equity,
arising under this Constitution, the Laws of the United States, and
Treaties made, or which shall be made, under their Authority;—to all
Cases affecting Ambassadors, other public Ministers and Consuls;—to
all Cases of admiralty and maritime Jurisdiction;—to Controversies to
which the United States shall be a Party;—to Controversies between two
or more States;— between a State and Citizens of another
State,—between Citizens of different States,—between Citizens of the
same State claiming Lands under Grants of different States, and
between a State, or the Citizens thereof, and foreign States, Citizens