Frank Bowman, writing at Slate Magazine, tells how and why:
But if Congress wants more, it need look no further than the firing of David Iglesias, former U.S. attorney in New Mexico. The evidence uncovered in Gonzales’ Senate and House testimony demonstrates that he fired Iglesias not because of a policy disagreement or a management failure, but because Iglesias would not misuse the power of the Department of Justice in the service of the Republican Party. To fire a U.S. attorney for refusing to abuse his power is the essence of an impeachable offense.