[navyblue]

Of course it is true that only Congress can declare war. But the present can order military action without the consent of Congress for a limited period of time as authorized by the War Powers act.

[Sunsong]

The War Powers Resolution of 1973 (50 U.S.C. 1541–1548) was a United States Congress joint resolution providing that the President can send U.S. armed forces into action abroad only by authorization of Congress or if the United States is already under attack or serious threat.

[jamaksin]

The last formal Declaration of War by the United States, under the specifications provided for by the US Constitution: June 5, 1942, against Bulgaria, Hungary, and Romania.

[FYI - Korea was called a UN Police Action and not a war.]