While many would like to see W gone, it may not be the best for the nation to go through another Presidential impeachment, and I'm not sure the votes would be there. However, under Article 2, sec. 4 of the Constitution, impeachment is not limited to the office of President or Vice President.
"Section 4.
The President, Vice President and all Civil Officers of the United States, shall be removed from Office on Impeachment for and Conviction of, Treason, Bribery, or other high Crimes and Misdemeanors."
"...all Civil Officers of the United States"
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