What they voted for
In all this talk about the build up to the Iraqi war, let's not forget what it is Senators actually voted for:
...Congress did not vote for the definite use of force, let alone for the removal of Saddam Hussein from power. It authorized the use of force if necessary to ensure that Iraq either gave up its weapons of mass destruction or proved it didn't have any.
In October 2002, when Congress passed the resolution, even Bush saw it (or at least indicated he did) primarily as a tactic for putting maximum pressure on the U.N. Security Council to pass a second, tougher resolution warning Iraq that it faced punitive action if it did not cooperate better with U.N. weapons inspectors. In a typical comment, two days after the resolution passed, Bush said, "But I am very firm in my desire to make sure that Saddam is disarmed. Hopefully, we can do this peacefully. The use of the military is my last choice, is my last desire."
While it seemed obvious to me at the time that we were headed for war if this vote passed, it did not mean that we unilaterally had to go to war. It simply gave the President the ability to do so if and when it proved necessary. And many of those who voted on the resolution then can argue that the President simply jumped the gun on the whole idea.
The only guilt that Democrats have to admit to is one of trusting the President. And that's something that most of America is feeling right now.