Democratic Consultants

This story from TPM is both all too common and, in my opinion, completely insane.

Former John Kerry adviser Jim Jordan allegedly told him in 2002 that he would "never be President" unless he voted for the Iraq War.

This was the "wisdom" of our pundits, consultants and leaders, that voting against the Iraq war resolution would be fatal. But why, what possible reasoning, lead to people believing with such certainty that that was the case? I mean had no one noticed that in 1992, after the Democratic party had in large measure voted against the first Gulf war resolution, Bill Clinton was elected President, as a Democrat. Given that history, why was it considered beyond question that an anti-war stance would be a deal breaker for a presidential candidate? Why?