Only one person was in a position to deploy troops to Iraq -- the Commander-in-Chief.
What Congress did was to authorize him to use force if he deemed it was necessary to protect us from "the continuing threat posed by Iraq," and that further diplomacy would "not adequately protect the national security" against that threat.
Only Bush never gave diplomacy the chance to work because in reality, he didn't want diplomacy -- he wanted to go to war. So he pulled the U.N. inspectors out of Iraq before they had the opportunity to complete their mission because during the time they were there, they hadn't found the smoking gun Bush was warning us about. He wasn't about to allow such pesky details interfere with his war agenda.
It was like handing Bush a gun and now blaming Democrats because he used it erroneously.