It's not as it was with President Nixon. The thought of Nixon is impossible except under the shadow of Watergate, which would have meant impeachment and probable conviction. But it isn't widely remembered that there was a movement to impeach Nixon before Watergate -- over the bombing in Cambodia. I remember a moment, in the course of a debate with Arthur Schlesinger Jr. before a huge crowd of students, when I ridiculed the idea of impeaching President Nixon.
"I never came out for impeaching him," Schlesinger said.
"Ah," said I, "but you are a vice president or whatever of Americans for Democratic Action, and they have come out for impeachment."
"I wasn't present at that meeting," Schlesinger said tensely.
An amusing and instructive aftermath came in the limo in which we were both driven off to a reception. Schlesinger sat in the back seat next to his mother, the widow of the hugely respected historian Arthur Schlesinger Sr. "Arthur," she said sternly, "you should not have come out for impeaching the president."
"Mother, I didn't. I wasn't even there."
What amused especially was Mother Schlesinger's refusing to take her son's word for it and sticking to her opposition. "Your father would never have come out for impeachment."
The dividing line is between just plain partisanship and Constitution-bending to advance a political cause. Several thousand convened in Washington last spring demanding the impeachment of President George W. Bush. The moving spirit of this enterprise turns out to be Ramsey Clark, who would be in favor of impeaching St. Peter if Peter gave out the least emanation in favor of a Republican president. So Clark continues to live in jerkdom, but that does not alter the fact that there are people out there who believe the time has come for impeachment.
The rules for impeachment were drawn up by a Constitutional Convention that was seeking means by which the checks and balances among the different branches of government might be enforced. The constitutional provision explicitly applies to "the president, vice president and all civil officers of the United States" -- which includes federal judges. Observers have sometimes wondered whether it also applies to members of the House of Representatives and the Senate, but the consensus has been that it does not. Then again, legislators can be removed, in extreme cases, by a two-thirds vote of their own house of Congress.