Things are seldom that straightforward. This current situation certainly isn't. In fact, courses of action are very seldom so starkly differentiated as you propose.
Don't get me wrong...I think, in retrosopect, the Bush Admin could have handled a lot of things differently, particularly selling the war and the occupation to the American public...and that things are not so cut and dried, hence my original post...that these legislators have to walk a fine line and there may be a lot more involved to their votes than merely the will of their constituents. There is a moral component to do what they feel is the right, or at least the best choice, amongst those that they are given...and there will be times when, if they are doing their jobs correctly, the would have to have the moral courage to go against the popular will...and their will be times they may find it necessary to oppose their own party. Having said all that, I think this choice is a relatively easy one, and voting with the dems on their "non-binding resolution," is a morally weak and indefensible choice that is against the interests of the nation at large.