In the joint interview on Late Edition on August 1:
"KERRY: <...>
The president did not exhaust all of the diplomatic remedies and the inspection process and the building of an international coalition so that, Wolf, number one, our troops would be safer. So that the chances of success for this mission would be higher. So that the cost to the American would be lower. "
<...>
"KERRY: You make this not a mistake. If I were president, I wanted the authority. I wanted to give that authority to President Clinton in 1998. I voted to give the authority, and if you read what I said on the Senate, I made it very clear what the expectations of the president were: Build an international coalition, exhaust the remedies of the United Nations and other countries, bring people to our side, and if you have to go to war, go to war as a last resort."
Edwards also spoke on the issue:
"EDWARDS: <...>
It was important, to answer the question specifically, it was important for the president to have the authority that he was given. I would have wanted John Kerry to have that authority if he had been president at the time. But the difference is, John Kerry would have dealt with this completely differently, and the result would have been very different.
He would have done the hard work to build international support for this effort. He also would have made sure we had a real plan to win the peace. We would not be in this place, we'd be in a very different place.
<...>
BLITZER: Let me rephrase it, the way the war was conducted, that was a mistake, was it?
EDWARDS: The way this president led up to the war and the fact that he had no plan to win the peace was an obvious mistake, yes."
http://www.cnn.com/TRANSCRIPTS/0408/01/le.00.html I think this is a good way, if not the only way, to counter the "but it's a good thing Saddam is gone" criticism.
To win the support of other Arab countries would have been a necessary precondition. Now that would have given you a long, long time for exploring other means to solve the problem. Just as Wes Clark once said, there was no reason to rush into war.
But excluding the war "a priori" would have given away the leverage.