Ross Douthat makes the point that a war can be "wrong" but popular, and that therefore anti-war senators shouldn't necessarily make the calculation that voting against a "wrong" war will have positive political ramifications:
[I]t's possible to think that a war will prove both misguided and enduringly popular. Maybe, as Matt suggests, Kerry and Edwards thought that Iraq would be a disastrous mess by 2004, in which case he's right: Their votes made no sense as policy or politics. But maybe they thought that the Iraq War was a bad idea because the doctrine of pre-emption set a dangerous precedent, or because they thought that invading Iraq was a distraction from the hunt for Bin Laden, or because they feared long-term blowback from further U.S. adventures in the Middle East - all of which would have been reasonable reasons to oppose the war, but none of which would have given them confidence that they would be vindicated in the court of public opinion any time soon.
I don't know how much sense it makes, though, to assume that anybody would vote against a pre-emptive, distracting, inflammatory war, if they thought that war was going be a tremendous success. After all, it's hard to imagine any war being "enduringly popular" if, two years in, there were few successes to show for it. In the case of Iraq, the president promised that liberty, democracy, and economic independence would take hold in Mesopotamia and that the magnetic effects of such massive improvements in Iraqi society would soon create a ripple effect across the entire Middle East. Well, a war that outrageously successful would probably obviate the concerns Ross mentioned--and pretty much any other concerns one might have--about ancillary costs! If I'd ever believed things were that simple and that everything would go according to plan, then I probably would have gotten behind the Iraq war and perhaps would endorse a variety of other pre-emptive military excursions in the future.
If we're talking about politicians with solidified opinions about the war, then there are four ways to permute this: Either they think the war is right and likely to succeed (vote for it!), they think the war is right, but likely to fail badly (probably vote against it), they think the war is wrong and likely to fail badly (vote against it!), or--and this is the important one--they think the war is wrong, but likely to succeed. If that's the case, then, for the reasons outlined above, they'd probably vote for it. The Shrum revelations imply that Kerry and Edwards fit into the third category, but voted as if they fitted in the fourth category. Which means that either Shrum is wrong altogether--that neither Kerry nor Edwards really knew how they thought war was going to go--or he's right, in which case it seems neither man devoted much serious thought to either Iraq or the more vulgar question of how their votes would affect their own political realities down the road.