The strongest argument against the Senate’s authority to try a former officer relies on Article I, Section 4 of the Constitution, which provides: “The 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.” The trial’s opponents argue that because this provision requires removal, and because only incumbent officers can be removed, it follows that only incumbent officers can be impeached and tried.
But the provision cuts against their interpretation. It simply establishes what is known in criminal law as a “mandatory minimum” punishment: If an incumbent officeholder is convicted by a two-thirds vote of the Senate, he is removed from office as a matter of law.
If removal were the only punishment that could be imposed, the argument against trying former officers would be compelling. But it isn’t. Article I, Section 3 authorizes the Senate to impose an optional punishment on conviction: “disqualification to hold and enjoy any office of honor, trust, or profit under the United States.”
Thus a vote by the Senate to disqualify can be taken only after the officer has been removed and is by definition a former officer. Given that the Constitution permits the Senate to impose the penalty of permanent disqualification only on former officeholders, it defies logic to suggest that the Senate is prohibited from trying and convicting former officeholders.