Abdicated their responsibilities? There was faulty intelligence floating around everywhere, so you can't exactly blame them. What should they have said at the time? "I don't believe it"?
Yes, they abdicated their responsibilities. It is Congress' job to declare war. They didn't do that. They voted to let the President invade, without a formal declaration. That is a clear abdication of their constitutional responsibilities. What makes it worse is that the evidence was so flimsy to begin with.