Far from being a flip flopper on Iraq John Kerry is guilty of mental rigidity.

I just read the speach he gave before voting to conditionally authorize Bush to use force in Iraq.

"And I believe they made it clear that if the United States operates through the U.N., and through the Security Council [snip] If the President arbitrarily walks away from this course of action--without good cause or reason--the legitimacy of any subsequent action by the United States against Iraq will be challenged by the American people and the international community. And I would vigorously oppose the President doing so.
[snip]
Let me be clear, the vote I will give to the President is for one reason and one reason only: To disarm Iraq of weapons of mass destruction, if we cannot accomplish that objective through new, tough weapons inspections in joint concert with our allies.
[snip]

I will support a multilateral effort to disarm him by force, if we ever exhaust those other options, as the President has promised, but I will not support a unilateral U.S. war against Iraq unless that threat is imminent and the multilateral effort has not proven possible under any circumstances. [snip] In voting to grant the President the authority, I am not giving him carte blanche to run roughshod over every country that poses or may pose some kind of potential threat to the United States. [snip] The threat we face today with Iraq does not meet that test yet. I emphasize "yet." Yes, it is grave because of the deadliness of Saddam Hussein's arsenal and the very high probability that he might use these weapons one day if not disarmed. But it is not imminent, and no one in the CIA, no intelligence briefing we have had suggests it is imminent. None of our intelligence reports suggest that he is about to launch an attack. "

This speach explicitely considers the possibility that Bush would abandon tough inspections because he wanted to invade Iraq for other reasons. Kerry said in advance that he would denounce such a course of action, which he clearly recognised was possible. Far from being inconsistent with Kerry's later position, the speach presents it in the hypothetical. The Republican operators who accuse Kerry of flip flopping have gone over this speach carefully. They are lying. No surprise there. Brave, honest, balanced and non partisan journalists would point out that their claims are lies, since there is no possible ambiguity.

Still Kerry's speach seems to me to be disconnected from reality. Did he really think that the wording of the resolution would make any difference ?

I think the problem is that, for political reasons, he decided to pretend that the difference between Bush and Clinton was not fundamental and decisive for all questions related to authorizing the President to do anything.
He should have known, he probably did know, that promises from Bush were worthless and that Bush would treat the resolution as "carte blanche to run roughshod over every country that poses or may pose some kind of potential threat to the United States." My sense is that he was making very sure that he had disproved in advance any attempt to call him a flip flopper if he later opposed Bush's choice to invade. Another problem might be the naive belief that rock solid proof that an accusation is false is worth something in US political debate.

I disagree entirely with Kerry's speach. I too believed that Iraq had chemical and biological weapons at the time. I considered that a strong argument against invading. Before the invasion I argued that an invasion would have enormously increased the risk of such weapons ending up in the hands of terrorists. Kerry did not even consider this obvious, and to me decisive, argument. I assume that the reason his argument is unsound is that he was voting yes for political not policy reasons, but it is just possible that he really didn't grasp that Bush was determined to invade Iraq and so, even if a credible threat would make Saddam Hussein cave (as it did) nothing would be gained. I hope he now understands who he is dealing with.