Executive orders can only work off pre-existing law. In the case of the "war on terror" everything Bush has done has been done in the framework of congressional law whether it was the establishment of a new cabinent position, the patriot act, guantamo bay, FISA courts, military action in Afghanistan, etc.
As it stands this country isn't operated by one person/position. I'm stating this hypothetically (and not really attempting to argue the point further so as not to thread jack), but if Bush is doing something illegally it is congress's fault along with the judiciary (not saying he did or didn't) for not checking his power and reigning him in. In regards to military conflict directly there are checks and balances, like in the past with the War Powers resolution (
http://en.wikipedia.org/wiki/War_Powers_Resolution) which establishes:
-regular consultation with the congress, and if possible consultation preceeding any military action, which would leave the door open for say a reactionary mission, but not a full scale invasion.
-a dossier submitted to the speaker of the house and pres. of the senate 48 hours following action stating necessity/circumstances, constitutional authority in which action was invoked and what legislative law gave made framework, and scope/duration of the mission
-Military action only has a 60 day window (where I quoted 90 earlier) following a written report to congress ^^. The operation can only continue by legislative authority (read declaring war or specific law), if congress is unable to convene as a result of conflict, or a possibly 1-time 30-day extension if "military necessity" requires it. Any concurrent congressional resolution can put an immediate end to action.
(The law in its entirity
http://caselaw.lp.findlaw.com/caseco...rs/33/toc.html)