The December 4th episode of
Intelligence Squared US asks that very question. It's an interesting debate that I strongly recommend.
Poll Is Bush the worst president of the last 50 years? Added: Before the debate started they polled the studio audience. The results were:
65% agreed
17% disagreed
18% were undecided
At the end of the debate they polled the studio audience again. Those results were:
68% agreed
27% disagreed
5% were still undecided