Congress has ultimate control via funding of the war. If Congress refuses to fund it, it won't continue.

[link|http://www.thenewamerican.com/departments/quotes/presidents_war_powers.htm|Cite]:

"Mr. Chairman, I think it is a fact of modern history that declarations of war are gone. I think they are anachronistic. I do not think they will happen. Clearly the Constitution assigns the declarations of war function to Congress and only to Congress. But declaring war has consequences in a technologically advanced world that nobody wants to face.... We have the untrammeled authority to unappropriate, disappropriate funds. That is the key; and that makes us the king of the hill."

Representative Henry Hyde (R-IL)
(Congressional Record, June 7, 1995)


But of course you already knew that. :-)

Cheers,
Scott.