In Iowa, according to The Times, Democratic hopefuls found a 'minefield' of anti war sentiment. Apparently Dean felt frustrated(?) and was forced into asking if anyone wanted to talk about something else. The audience was throwing an issue at him and he was trying to ignore it.

At some level this has to do with money. The Republican base and financial backers share ideologies, as much as the two sides of a coin share the coin. Working class Republicans vote against their own interests for reasons of romance. Rich Republicans vote for what they want. Wealthy Democrats on the other hand vote against their interests for reasons of what they consider decency or, at least, noblesse oblige. It's the Democratic middle class and below that vote their interests outright; and as a result while rich Republicans are hard Republicans, rich Democrats are soft Democrats. Their ideals are a luxury, not a necessity. They don't need health insurance or a fair minimum wage, they merely believe in them on principle, which is not the same thing. But Luxury Democrats have to be placated, while the base loses out.
Very few people live their principles by choice.

Dean and the others are not merely cowards, though they are, they are also almost always trapped. [And then again, they are wealthy themselves, aren't they?] And when they're not trapped, they're so used to being hemmed in that they remain frozen even when there is room to move.