And BTW Greggie boy, there is a historic precedent for impeachment after resignation.

In 1876, Secretary of War General William Belknap, accused of accepting a bribe, resigned just hours before the House was scheduled to consider articles of impeachment. The House went ahead and unanimously impeached him, and by a vote of 37-29 the Senate rejected the argument that Belknap's resignation should abort the case. The Senate proceeded with the trial, but Belknap was narrowly acquitted. A number of the Senators who voted for acquittal explained that they felt they lacked jurisdiction because of his resignation. (Incidentally, Belknap is the only cabinet member ever impeached.)

By contrast, when in 1926 Illinois District Judge George English, impeached for various acts of wrongdoing, resigned from office six days before the scheduled commencement of his trial in the Senate, the matter was discontinued. The same was true, of course, when Richard Nixon resigned just prior to adoption of articles of impeachment by the House.

The Belknap precedent aside, is there any logic to impeaching and trying an official who is no longer in office? One answer might be the value of establishing a precedent that certain misconduct is (or is not) impeachable. But there's a more direct, practical reason why Congress might choose to proceed even after a resignation. As we have seen, one potential punishment of impeachment is disqualification from future office. Suppose an embattled president resigned, with an eye towards running in the next election. To preclude this possibility, Congress might choose to go ahead and impeach, try, and convict the President, and disqualify him from holding future office.

Evidence suggests that the Framers of the Constitution concurred in this conclusion -- they did not regard resignation as automatically precluding impeachment or conviction.