Can ex-presidents be impeached? No. Convicted? Yes.

Can a former U.S. president be impeached? Can he be convicted?

Those are two different constitutional questions. And U.S. President Donald Trump, impeached last week while still in office and potentially subject to conviction after departing, has obvious reason to offer a firm “no” to the second question.

Under the Constitution, the House of Representatives is authorized to impeach a president, and then the Senate is authorized to convict him. But that doesn’t answer the questions about a former president.

Let’s start with the text. Article I says this: “Judgment in Cases of Impeachment shall not extend further than to removal from Office, and disqualification to hold and enjoy any Office of honor, Trust or Profit under the United States: but the Party convicted shall nevertheless be liable and subject to Indictment, Trial, Judgment and Punishment, according to Law.”

Article II says this: “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.”

Under these provisions, it should be clear that the House cannot impeach someone who has never held public office, and who merely aspires to do so.

Suppose, for example, that a presidential candidate has done horrible things while, say, serving as governor of a state. The text makes it clear that impeachment is unavailable.

What about an ex-president? Could the House, now or next year, impeach Jimmy Carter? Bill Clinton? George W. Bush?

The Constitution doesn’t explicitly answer this question, but there’s a strong argument that the best answer is, No.

The overriding goal of impeachment is to start a process that can culminate in removal from office. If a president is no longer in office, he can’t be removed. The main point of the impeachment clauses is to allow “We the People” to take action, in real time, against officials who are egregiously abusing their authority. If a president is a private citizen, that purpose of the clause no longer appears relevant.

There is a counterargument, which is that Article I refers not only to removal, but also to “disqualification to hold and enjoy any Office of honor, Trust or Profit under the United States.”

If an ex-president is deemed to have committed impeachable offenses, perhaps it would be perfectly legitimate to impeach and remove him — and thus to block him from running for president (or other office) ever again.

The counterargument isn’t crazy. It receives some support from the leading precedent, the impeachment of Secretary of War William Belknap in 1876. It’s a fascinating tale, ably told by my Bloomberg Opinion and Harvard Law School colleague Noah Feldman.

Belknap resigned just hours before a House committee recommended his impeachment. In the ensuing debate, the House explored, in detail, whether it was permissible to impeach someone who was no longer in office.

When it voted to impeach Belknap, the House essentially concluded that a post-resignation impeachment was permissible. In the Senate, Belknap’s lawyer insisted that he was a private citizen and so could not be tried. By a vote of 37 to 29, the Senate rejected that argument. A majority of the Senate — but not the necessary two-thirds — voted to convict Belknap.

There are two problems with reading the Belknap debates to resolve the question whether a former president can be impeached and convicted. First, the House and Senate might have gotten it wrong; their disputed judgments, way back in 1876, are hardly conclusive. Second, Belknap resigned immediately before a House committee was going to recommend his impeachment. This was hardly analogous to a decision, in 2021, to pursue Carter, Clinton or Bush.

Turn in this light to the unique question that is about to face the Senate. After the unquestionably legitimate House impeachment of a sitting president, can the Senate proceed to convict him after he leaves on Jan. 20, the day of Joe Biden’s inauguration, and becomes a private citizen?

You could easily argue that it can. In impeaching Trump, the House did its constitutional duty. If the Senate proceeds to a trial, it is merely continuing the process. And for the Senate to complete that process is not at all pointless, even if Trump is no longer president. The disqualification provision makes that clear.

The counterargument is also not hard to sketch. Once Trump has left office, he cannot be removed. Removal is the central goal of the impeachment provision.

The argument for allowing the Senate to try Trump is far stronger than the argument for allowing the House to impeach, and the Senate to convict, someone who has been out of office for a long time. It is even stronger than the argument for allowing the Senate to try Belknap, because Trump was impeached while he was in office.

Still, the Constitution does not clearly resolve the central question; it contains a genuine gap. Someone has to fill it. The impeachment process has obvious political dimensions, and the Supreme Court is highly unlikely to get involved.

Which means that the Senate is the right institution to fill the gap. Without offense to the Constitution, it could choose to stay its hand. Without offense to the Constitution, it could choose to complete the process that the House started.

If the Senate wishes to convict Trump, it can.

Cass R. Sunstein is a Bloomberg Opinion columnist. He is the author of “Too Much Information” and a co-author of “Nudge: Improving Decisions About Health, Wealth and Happiness.”