Scandal in Washington has its own rhythm and its own rules. Take the US Attorney firings, for example. At this point in the scandal, with Attorney General Alberto Gonzales cover story having been completely blown and new details emerging daily and Republican support eroding - its clearly time to go. A cabinet official in the Bush I or Clinton administrations would have been canned a week ago. Gonzales is radioactive.
Bush has gained a lot by breaking the unspoken rules of Washington. He acted like he had a conservative mandate when he should have acted humble after the 2000 election. He crosses all kinds of red lines when he campaigns - "Elect Democrats and the terrorist will kill us all." Completely ignoring the policy process in favor of politics.
But breaking this rule will cost him. You've got to dump people. Its how you end a scandal or at least get it under control. The longer he clings to Gonzales, the more he will sink. And he doesn't have much further to sink.