After President Nixon resigned, was any serious consideration (e.g. by members of Congress or important opinion leaders) given to proceeding with his impeachment and trial? The motive, of course, would have been to seek the maximum penalty of "disqualification to hold and enjoy any Office of honor, Trust or Profit under the United States." (Quoted from Article I, Section 3, Clause 7 of the U.S. Constitution.)
Edit. In the answer by sds it is asserted that the U.S. Constitution does not permit the impeachment of an official who has resigned. That assertion is probably wrong. (I am not a lawyer.) The precedent is the case of William Belknap, Secretary of War under President Grant. Quoting the Wikipedia article:
On March 1, Belknap and his counsel went before Clymer's committee, but Belknap declined to testify. On the morning of March 2, Treasury Secretary Benjamin Bristow told President Grant of Belknap's impending impeachment. In a White House meeting soon afterwards, Grant asked for Belknap's resignation. This move was clearly an effort to forestall the pending impeachment proceedings; by resigning first, Belknap could argue that Congress had no authority, since he was no longer in office. Grant accepted Belknap's resignation at 10:20 A.M. Clymer's committee was informed at 11:00 A.M. Although Belknap's resignation caused great commotion among House members, it did not prevent action by the Clymer committee. The committee unanimously passed resolutions to impeach Belknap and drew up five articles of impeachment to be sent to the Senate. Belknap, by then a private citizen, was impeached by a unanimous vote of the House of Representatives. Speaker of the House Michael C. Kerr wrote to the Senate that Belknap resigned "with intent to evade the proceedings of impeachment against him." Belknap's case was constitutionally unprecedented and would serve as reference for nine other civilian officials' resignations before trial, including President Richard Nixon.
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Starting on April 5, 1876, Belknap was tried by the Senate, which was presided over by Supreme Court Chief Justice Morrison Waite. For several weeks Senators argued over whether the Senate had jurisdiction to put Belknap on trial since he had already resigned office in March. Belknap's defense managers argued that the Senate had no jurisdiction; the Senate ruled by a vote of 37-29 that it did. With 40 votes needed for conviction, the Senate voted 35 to 25 to convict Belknap, with one Senator not voting, thus acquitting Belknap by failing to reach the required two-thirds majority