Could Congress annul a declaration of war from the U.S. President? Let's say that the President declared war against Cuba for no reason, could Congress step in and annul the declaration of war or is the President's prerogative to declare war on any country absolute in American law? Is there really no recourse whatsoever?
Under the U.S. Constitution, only Congress can declare war. The declarations used to be in the form of a bill that was subject to presidential approval or veto.
The War Powers Act was enacted at the end of the Vietnam War. It purports to allow Congress to extract the country from wars de facto started by the President as Commander-in-Chief. The last time I checked (many years ago), every president (including Carter) considered the War Powers Act to be unconstitutional even as they complied with the paperwork the Act mandates.