[onetimemanytime]

Congress has given the President this power, as the article says:

https://www.law.cornell.edu/uscode/text/50/1701

"(a) Any authority granted to the President by section 1702 of this title may be exercised to deal with any unusual and extraordinary threat, which has its source in whole or substantial part outside the United States, to the national security, foreign policy, or economy of the United States, if the President declares a national emergency with respect to such threat."

USA has given its President a lot more power over the years and decades.