At the same time, it would take a brave man (and the Chris Shays of the world are not) to buck G.W. Bush from this point on. Without GOP support, or worse a statement that "this is no longer our guy" would be the kiss of death even for a safe seat.
Then perhaps you can offer some other reason as to why, for all the President has accomplished, and for all that the Congress has done, their approval ratings are in the toilet. I really think the perception of scandal has eroded support over time, and that, while none of these scandals has led to a resignation from the Administration or Congress, the collective weight has worn down their approval ratings.