Declare War  The Congress shall have Power To ...declare War....
Article I, Section 8, Clause 11  It is well accepted that the
conduct of war is an "executive Power," vested by Article II in
the President, who also serves as Commander in Chief of the
Armed Forces. Both at the time of the Framing of the
Constitution and afterward, there has been agreement that the
President has the power to repel invasions. Intimately familiar
with the treatises on international law, the Framers were
undoubtedly aware of the general rule that, as Hugo Grotius had
put it, "By the law of nature, no declaration is required when
one is repelling an invasion." The Law of War and Peace (1646).
The debate, instead, has centered on the location of the power
to initiate war.  Advocates of congressional power contend that
the President cannot initiate hostilities because the
Constitution expressly vests the power to "declare War" in
Congress. In support of that view, they note that, according to
his notes from the Constitutional Conven