"This is a prescription for chaos and confusion and we must not impose it on our troops," Bush said in a nationally broadcast statement from the White House. He said the bill would "mandate a rigid and artificial deadline" for troop pullouts, and "it makes no sense to tell the enemy when you plan to start withdrawing."

http://www.bostonnow.com/news/nation/2007/05/01/bush_vetoes_troop_withdrawal/

I feel as if the logic doesn't work, perhaps someone can help me if I'm wrong:

If it makes no sense to tell the enemy when you plan to start withdrawing then either you withdraw unexpectedly (by surprise), or you never withdraw. Those are the only ways "the enemy" (enemy of who?) won't know when America's troops are withdrawing.