Special counsel Robert S. Mueller III. (Saul Loeb/AFP/Getty Images)

David M. Dorsen served as assistant chief counsel of the Senate Watergate Committee and as an assistant U.S. attorney in the Southern District of New York. He is the author of “The Unexpected Scalia: A Conservative Justice’s Liberal Opinions.”

On Oct. 10, 1973, Spiro T. Agnew, pursuant to a plea bargain, resigned as vice president and pleaded guilty to one count of tax evasion. He was sentenced to a fine of $10,000 and a period of unsupervised probation. Agnew famously had participated in a bribery and extortion scheme for many years as a county executive and then governor of Maryland. Packets of cash were even delivered to Agnew in the White House. The rationale for this plea agreement was to avoid the intolerable situation of Agnew’s ascending to the presidency as a result of the impeachment and conviction of President Richard M. Nixon in connection with the simultaneous Watergate scandal.

Commentators here and elsewhere have cited this outcome as a possible precedent for the removal of President Trump, although most recognize that in his case there probably would be no guilty plea and that he and his family would receive immunity. The alternative would, to put it mildly, be traumatic and messy. The deal would give the country an untarnished president.

While salutary, however, I believe that such a deal would be both unconstitutional and destructive of our system of government. Whatever one might think of Trump as a human being and leader, he was elected president of the United States in conformity with the Constitution. The Constitution provides one method and one method only for removing the president, namely by impeachment by a majority of the House of Representatives and conviction by two-thirds of the Senate. Only the combined houses of Congress wield the enormous power of removing a sitting president.

However one may view the circumstances of Agnew’s removal, we cannot ignore the fact that in the case of a president, such a plea agreement would seem to permit unelected prosecutors to facilitate, if not coerce, the removal of a duly elected chief executive of the United States by offering criminal-law inducements. That is not how the Constitution should operate. The tenure of a sitting president should not be controlled by a prosecutor armed with a sympathetic grand jury.

Removal of a president by plea bargain, moreover, obviously contains seeds of abuse. A single U.S. attorney could decide to threaten a president with indictment. If there were sufficient evidence, or else a president who lacked the spine or evidence to fight the indictment, we would have a situation in which the president might choose to take his marbles and go home. Extortion might work. So might a case in which a president is delighted to make a deal with his attorney general that lets him escape prosecution for serious crimes, by the simple act of resigning.

While the Justice Department takes the position that a sitting president cannot be indicted, its view is not backed up by established law. No one knows if that position is correct, though most scholars and the department accept it (as do I, though I’m less sure about a sealed indictment against a president that is not disclosed). If ever put to the test, the courts, over a period of months if not years, would decide the issue. Meanwhile, the president would be under indictment and the country vulnerable to a variety of threats.

However that question is settled, the attorney general should take the position that the Constitution prohibits the Justice Department, including special counsel such as Robert S. Mueller III, from negotiating the resignation of the president. That would mean that Trump could not avoid criminal indictment for himself — whether immediately or when he finally leaves office — by trading the office of the presidency for a pass from prosecution for serious federal crimes for him and his family.

The consequences of my view might mean that Trump would remain president longer than otherwise. But it would also mean that Trump and his family would be held accountable for their criminal conduct. And it would reinforce the structure of our Constitution as formulated by the Founders.

Read more:

Hugh Hewitt: Impeachment? Don’t hold your breath.

Jennifer Rubin: Impeachment talk? Let’s have at it.

Megan McArdle: Who’s most at risk from the Russia investigation? It just might be the Democrats.

44 Former U.S. Senators: We are former senators. The Senate has long stood in defense of democracy — and must again.

Dick Thornburgh: We Republicans must all speak out to protect the Mueller investigation