In reality "the scream" wasn't why he didn't end up the Democratic nominee in 2004. Before the Iowa Caucus Dick Gephardt's campaign really went negative and attacked Dean constantly. Dean reciprocated by attacking Gephardt and so Dean's and Gephardt's were in an intense mudslinging battle. That turned Iowa voters off and they turned to Kerry who looked the most presidential and electable. Had Kerry not been from New England like Dean, Dean likely would have won the New Hampshire primary scream or no scream.
Gephardt's support came mostly from labor unions and Dean's supporters were mostly white liberal academics. And they just clashed leading into the Iowa caucuses. It got so nasty I think a fist fight broke out in front of somebody's house while both campaign's volunteers were our canvassing.
Dean's campaign had started to lose steam before the Iowa caucus and he likely knew that, which is why the scream happened in the first place. The media through it way out of proportion of course.
This is pretty much the truth. Gephardt had to win Iowa or he was cooked, so he attacked Dean the frontrunner who responded in kind. Dean could have, had expectations been lower, afforded to lose Iowa and move on to New Hampshire, but he was the hot candidate who came from nowhere and piled up a ton of big endorsements including Al Gore. As a result, his expectations in Iowa were also very high. The result was Mutual Assured Destruction and a Kerry win, after which he won New Hampshire and pretty much wrapped up the nomination then and there. Worth noting: the scream came the night he lost Iowa, which was the beginning of the campaign unraveling.
The other thing that hurt Dean was that while he was raising money left and right on the internet, it was going out the door just as fast, which put pressure on them to wrap things up ASAP as they just didn't have the money for a long slog through the primaries.
So, in the grand scheme of things, the "scream" was less important than is generally believed.