It doesn't seem to me that the loss of the middle 40% is due to any of the failures of the antiwar movement. It seems to me that the loss of the middle 40% is due to three things:
--First, the success of the Bush Administration in blurring the distinction between "Saddam Hussein supports terrorism" (large payments to families of people who blow up Israelis in shopping centers) and "Saddam Hussein is allied with Al Qaeda and is a threat to the United States." Once that distinction is lost--once the distinction between the U.S.'s war on Al Qaeda and its ilk and Israel's war against those in the Arab world who want to see the country driven into the sea and a lot of dead Jews disappears--a lot more people are going to be in favor of overthrowing Saddam Hussein (and Bashar Assad, and the House of Saud, and the Theocrats of Tehran: this is a very dangerous road we are starting down--one in which forces that want to destroy Israel are automatically seen as Osama bin Laden's comrades-in-arms).
--Second, the success of the Bush Administration in portraying U.N. opposition as due to Jacques Chirac's intransigence--that Chirac is simply uninterested in any form of effective containment of Saddam Hussein no matter what, and his ability to block U.N. action means that the U.N. cannot be taken seriously here.
--Third, the fact that the neocons turned out to be closer to being correct about the social bases of Saddam Hussein than they had any right to be. I expected nationalism plus anti-imperialism plus Arab unity to give Saddam Hussein considerable forces in this war. But they didn't. There were some Fedayeen Saddam willing to fight--but they were untrained, early-era Brownshirt types who had watched too many Rambo movies and rushed tanks armed only with rifles. There were some Republican Guards willing to die in place--but many fewer than even observers like Kenneth Pollack thought.
The first and second of these seem to me to be failures at the level of the media, not at the level of the antiwar movement, which I think did a fairly good job of mobilizing people in support of the antiwar case. So I wouldn't blame the antiwar movement at all, given the context in which it was operating.
Brad DeLong