From Slate.com, 3-15-7

The White House and DoJ are now under fire because, in disrespecting the post of U.S. attorney, they appeared to interfere with the independence of that office in a way that's unprecedented. In the previous quarter-century, according to the Congressional Research Service, no more than five and perhaps only two U.S. attorneys, out of 486 appointed by a president and confirmed by the Senate, have been similarly forced out—in the middle of a presidential term for reasons not related to misconduct. "It would be unprecedented for the Department of Justice or the president to ask for the resignations of United States attorneys during an administration, except in rare instances of misconduct or for other significant cause," White said when she testified in February about the Bush firings before much was known about them.