Is it constitutional to hold an impeachment trial for a former president?

No one knows whether the Constitution permits the Senate to hold an impeachment trial for former President Donald Trump, now that he no longer holds office.

To be sure, there is a bevy of legal scholarship discussing this question. And, as a recent report by the nonpartisan Congressional Research Service notes, “most scholars who have closely examined the question have concluded that Congress has authority to extend the impeachment process to officials who are no longer in office.”

But while the Constitution mentions impeachment six times, the text of the...