I really want to know how you impeach someone who is not longer in office. I have yet to have anyone explain it to me.
There's precedent https://www.nbcnews.com/politics/meet-the-press/meet-other-american-who-was-impeached-tried-after-leaving-office-n1255516 and a policy argument: The power to impeach must be applied to all times that the pres occupies office even if enforced afterwards or the evils to be punished could be avoided by simple minded resignation just as the trial is set to conclude.
EDIT:
The Constitution, in fact, is silent on the question of who is subject to impeachment. Luttig cites the clause in Article II providing that “[t]he President, Vice President and all civil Officers of the United States, shall be removed from Office on Impeachment for, and Conviction of, Treason, Bribery, or other high Crimes and Misdemeanors.” All this clause “clearly” establishes is a mandatory punishment (removal from office) for current officers. It does not even purport to address whether the impeachment power extends to former officers, let alone whether an officer who is subject to impeachment proceedings may evade punishment by leaving office. The clauses that define the ambit of the impeachment power are found in Article I and make no mention of the limitation Luttig reads into the Constitution’s text. Article I assigns to the House “the sole power of impeachment” and to the Senate “the sole power to try all impeachments.” Nothing in this assignment of authority excludes former officers. While the Constitution’s text may be ambiguous, the original understanding and subsequent congressional practice emphatically establish that a former officer is subject to the Senate’s “sole power” to try impeachments. As Alexander Hamilton makes clear in Federalist No. 65, Great Britain provided “[t]he model from which the idea of this institution has been borrowed.” It was firmly established in Britain at the time of the founding that former officers were subject to impeachment. Indeed, the British impeachment that most informed the Framers’ thinking about the impeachment power was the impeachment of Warren Hastings for improprieties as the governor-general of Bengal. Hastings had been out of this office for two years before his impeachment by the House of Commons. Moreover, at least two states—Virginia and Delaware—had established that their impeachment power extended to former officers. Against this background, it is particularly telling that there is no indication in the Federalist Papers or in any other significant commentary from the founding era indicating that the Framers intended the new Constitution to deviate from this baseline understanding. Congress has also expressly addressed this question and resolved it in favor of the original understanding. In 1876, the House drafted articles of impeachment against President Ulysses S. Grant’s Secretary of War, William Belknap, but Belknap resigned before the House could vote on the articles. The House debated whether Belknap’s resignation deprived the House of jurisdiction. After the debate, the House voted to impeach Belknap, implicitly rejecting the argument that it lacked jurisdiction. The Senate also took up the issue and voted 37–29 that Belknap’s resignation did not deprive it of jurisdiction.
(post is archived)