It is not difficult to imagine the following events coming to a head in the near future:
Crude at $100 leading to $3.50 gasoline at the pump and an economic contraction.
Failure to achieve Iraqi constitution and the dissolution of the country into civil war by militias.
Continued American combat losses by increasingly proficient insurgent roadside bombers.
Indictments of Rove, Libby, et. al. by Fitzgerald, with potential imputation of fraud by administration on war justification claims.
With Bush at 33% approval, might not some people be entertaining the thought of short-circuiting his presidency via impeachment?