Consider this hypothetically. President Bush's surge in Iraq does not work and fatalities rise. Democratic & some Republican politicians make a lot of noise and impeach Bush. Then what?
Dick Cheney takes over as President, but isn't he the guy who promised rose petals for American soldiers in Iraq, so the Congress impeaches him too. Then what?
The next in line, Speaker of the House - Nancy Polosi takes over as President and America has a woman President after all. Then what? After a year or so in the job, she says she likes it and decides to run for President in 2008.
The question is, do Senators Clinton, Obama and Biden on the Democratic side and Hagel, Brownback & McCain on the Republican side want to coronate Nancy Polosi as President, only to taker her on in 2008? I think not. President Bush has nothing to fear.