With special counsel Robert Mueller’s Russia investigation reportedly nearing its end, it is worth considering how President Donald Trump might be removed from office before his term ends. The first way is the well-known method of impeachment. The second is removal for disability under the 25th Amendment. With those two outcomes seeming increasingly unlikely, a third previously unexplored possibility has entered the conversation recently: that through a plea bargain, Trump would resign in exchange for lenient treatment by the Department of Justice.

As mentioned, the first two are highly unlikely absent extraordinary developments. Impeachment would require a two-thirds vote of the Republican-controlled Senate. Removal for disability would require the vote of the vice president and a majority of the Cabinet.

The third method, under discussion since recent revelations about the extent of the president’s possible criminal liability, was employed during the Watergate era to prevent Vice President Spiro Agnew from potentially succeeding President Richard Nixon. Agnew had a history of taking bribes as a Maryland county executive, as governor of Maryland, and as vice president—Agnew even accepted bribes in the White House. His indictment was anticipated. Obviously, few wanted him as president. Moreover, Agnew’s presence discouraged some from seeking Nixon’s removal.

On Oct. 10, 1973, though, Agnew resigned and pleaded nolo contendere (no contest) to one count of tax evasion. He was sentenced to a fine of $10,000 and a term of unsupervised probation. House Minority Leader Gerald Ford was selected to replace him.*

In the event that Trump agreed to proceed on such a course, it is to be expected that the agreement would be more generous to him, possibly excluding a plea of nolo contendere and including immunity of his immediate family in the bargain. Vice President Mike Pence would become president, and a new vice president would be selected.

While that all seems fairly clean, I believe that a plea bargain to secure Trump’s resignation would be unconstitutional. While I cannot point to any specific provision of the Constitution or any court decision, my conclusion flows in large part from the structure of the Constitution, which specifically provides for removal by impeachment or because of a disability, as well as from the move’s practical implications. Whether a president can even be indicted is still a matter of public debate, but it does not seem to matter whether the Constitution permits indictment of a sitting president for the purposes of such a deal. To my knowledge, no one raised a question about the constitutionality of the Agnew bargain in 1974.

A resignation by threatening disclosure of criminal conduct likewise would be a crime.

To illustrate the problems associated with a plea bargain, we should first consider the hypothetical case of a private citizen paying a president to resign. That would clearly be bribery, which is paying something of value to a government official or employee to take official action. A resignation by threatening disclosure of criminal conduct would likewise be a crime. A voluntary resignation is different from a resignation produced by bribery or extortion.

What then gives an unelected federal prosecutor, whether the attorney general or a U.S. attorney—both presidential appointees—the power to obtain the resignation of a chief executive elected pursuant to the Constitution by exonerating him from criminal conduct totally, or ameliorating the seriousness of the crime or sentence? Similarly, why should a prosecutor be able to extort a resignation with the threat of filing an indictment? Further, why should a prosecutor be able to unilaterally let a criminally liable president off the hook? Imagine a different scenario where a prosecutor could effectively grant a soon-to-be ex-president immunity in a sweetheart deal in exchange for his resignation, perhaps in the last week of his term.

A federal prosecutor has the power to secure punishment for a crime, namely, prison and a fine, but nothing authorizes him to change the country’s leadership because he is convinced that there is probable cause to believe a president is guilty. Nothing in the Constitution or its structure gives executive-branch employees the power to reverse the results of an election and remove a president. That is a power reserved for Congress or the Cabinet. Consider the situation of a president pleading guilty to a crime and the judge ordering him to resign as president as part of the sentence. Do we think that would be an appropriate use of a single unelected judge’s power?

Finally, should the attorney general authorize a plea bargain and allow Trump to resign in exchange for immunity, that would not end the matter. After Trump’s resignation, a prosecutor could file an indictment against him and leave it to the courts to decide whether the Constitution nullified the plea bargain. There would be a cloud over the deal, which could end up giving Trump—and the nation—little other than years of litigation.

Correction, Jan. 31, 2019: Due to an editing error, this piece originally misidentified Gerald Ford as speaker of the House. He was House minority leader in 1973.