A number of political observers, notably Josh Marshall, have been singling out Giuliani's campaign as potentially being the worst in modern presidential history. After all, Giuliani was the national poll leader among Republicans for all of 2007. Suddenly, his support is bottoming out in state after state.
I don't think this is a fair characterization. The assumption is that the campaign got him to the point of being the top GOP candidate all during 2007 and then somehow blew that lead. That's not what happened. Giuliani's lead in last year's polls was based on very thin gruel -- high name recognition (relative to the other candidates, save McCain) and 9/11 hagiography. The campaigns inevitably force voters to learn more about the candidates. Not surprisingly, as Republicans learned more about Giuliani (his stances on social issues, his mixed record as mayor, his personal foibles), they found there wasn't that much there for them to like. You could see this happening in late '07, when he was still the national poll leader, but had dropped precipitously in the early primary and caucus states, where voters were paying closer attention.
This is not to overlook some weaknesses in his campaign, particularly his over-reaching advertisements, but even a really well run campaign probably couldn't have saved him.