I've tried to distill all of the salient points of Kerry's stance on Iraq into as few words as possible. Its inspired largely by comments and daries I've read here on dKos (special thanks to JeffLieber's inspiration for the last line).
"The vote by the Senate was a vote to support the President and give him the authority he needed to negotiate with the UN and Iraq from a position of strength. It was not, as the President and many others have said, a "vote for war" -- check the record and you'll find that the President himself called it a "vote for peace". It was my hope, and the hope of many of my colleagues, that the President would use this authority to bring Saddam Hussein back into compliance with the UN resolutions requiring inspections and disarmament, neutralizing him once and for all. And it did work, before the President lost patience and needlessly invaded Iraq and alienated our allies in the process. Now our military is bogged down in Iraq and there's no end in sight, and we have no trump card left to play when dealing with Iran, North Korea, Packistan and any other real threats to our security.
In short, I voted to trust the President to protect the United States without needlessly squandering our military, economic and political assets. And now I'm running for President because I believe that George Bush no longer deserves that trust. If that makes me a flip-flopper, then so be it."