Enemies of the United States, foreign and domestic.
If a group is designated enemy of the state it's an executive power.
In the Prize Cases, 1862, the Court said whether the President "in fulfilling his duties as Commander in Chief" had met with a situation justifying treating the southern States as belligerents and instituting a blockade, was a question "to be decided by him" and which the Court could not question, but must leave to "the political department of the Government to which this power was entrusted."
The Supreme Court rejected the argument that only citizens of foreign nations could be “enemies”
Additionally, The existence of a war is not dependent on legislative sanction.
Additionally, while Congress has the power to declare war, Congress passed laws granting the president the authority to use military and naval forces to suppress insurrection and invasion.
According to the Supreme Court, for there to be war for the purposes of the president’s war power, it is not necessary that both parties are acknowledged as independent nations.