HOUSE EMISSARIES delivered to the Senate on Monday an article of impeachment against former president Donald Trump, setting the stage for an unprecedented trial of an ex-chief executive. As they were sworn in as jurors on Tuesday, Republican senators appeared to be splitting into three groups: those arguing Mr. Trump’s actions do not warrant impeachment; those open to convicting him; and those claiming that the former president cannot be tried because he is no longer in office. It is with this last camp that Mr. Trump’s fate likely resides. Most GOP senators voted unsuccessfully on Tuesday to force a debate on the constitutionality of trying Mr. Trump.

Their theory — that impeachment applies only to sitting officials — is not beyond the pale. But it runs against the weight of scholarship, historical practice and common sense. Many Republicans may be embracing the theory nonetheless because it gives them an excuse to avoid any responsibility: They do not have to condone the former president’s incitement of the Jan. 6 Capitol invasion, but they also do not have to anger his supporters. Put briefly: They continue to indulge Mr. Trump’s toxic influence on their party.

There have been so few impeachments over the course of U.S. history that major issues such as this remain unsettled. But the Congressional Research Service notes that the nation’s Founders appeared to accept that former officials could be impeached for their conduct in office, as they could be in the British tradition. Decades later, while sitting in the House, former president John Quincy Adams declared, “I hold myself, so long as I have the breath of life in my body, amenable to impeachment by this House for everything I did during the time I held any public office.” In 1876, the House impeached former secretary of war William Belknap, who had resigned just before impeachment proceedings could begin. Both the House and Senate debated whether Mr. Belknap could be impeached and tried, and both chambers agreed he could be.

The Belknap affair highlights two crucial points. First, it would be illogical if Congress could impeach and punish only sitting officials, because then those officials could simply resign to escape any consequences, such as being barred from serving in federal office again. Officials at the very end of their terms also could engage in flagrant behavior without fear of punishment.

Second, absent clear constitutional instructions, Congress itself has wide authority to interpret the boundaries of the impeachment powers vested exclusively in the legislative branch of government. No outside authority has bound senators to a specific, implausible reading of the Constitution. Given that Congress may deem it essential — now or later — to bar an individual from federal office, it would be unwise for senators to set a precedent today that would hollow their authority in the future. Senators can and should proceed to the question of whether Mr. Trump should be convicted, and they each should take a stand on the merits.

Some might conclude that barring Mr. Trump from office could make him a martyr and do more harm than good. If so, they should be prepared to explain how they would deter future such depredations, with censure being the most obvious, minimally acceptable alternative response to Jan. 6. What they should not do is dodge, weave and try to move along as though nothing happened.

Read more: