How far can the Republican candidates distance themselves from Bush?

I agree with Fz's point below that the Republican aren't doing themselves any favors in '08 by refusing to criticize Bush. However, it's important to distinguish between the general election and the Republican primary. I would certainly admire the political courage of any primary candidate who'd dare to pull a Chuck Hagel and give Bush some frank criticism. Unfortunately, this would be political suicide in the primary. Bush is still popular with the Republican base. The candidates have to know that embracing Bush now will hurt them in the general election, but they have no choice.