Photo: Drew Angerer/Getty Images The second impeachment trial of Donald Trump presents a series of unusual constitutional questions. There is little argument about the facts of the case: Donald Trump repeatedly tried to overturn the results of the 2020 election and then, on January 6, 2021, egged on a crowd that would later storm the Capitol, terrorize lawmakers, damage historic property, and kill a policeman. Instead, the debate and Trump’s likely defense have pivoted on questions of law. Can a federal official be impeached after leaving office? And were Trump’s actions an impeachable of...