If President Donald Trump were convicted by the Senate in an impeachment trial and removed from office, could he still run for president in 2020? The possibility is remote, but the candidacy of a former President Trump could happen unless the Senate takes steps to prevent it.

The process bears examination because it has never been used before. No U.S. president has ever been convicted of an impeachable offense by the Senate. Andrew Johnson and Bill Clinton were both impeached by the House and acquitted by the Senate. Richard Nixon resigned before the full House could vote to impeach him.

Let's begin with the Constitution itself. The American framers adapted impeachment from British parliamentary practice, in which it was sometimes thought necessary to ensure that a royal official hurled from office could not rise up later and destroy his destroyers. Therefore, conviction by the House of Lords could mean being impoverished, imprisoned or executed.

The Philadelphia delegates of 1787 wanted no transplantation of such cycles of vengeance. They embraced impeachment as necessary to protect against a president whose failings or misdeeds endangered constitutional order. But they consciously limited the consequences of conviction to "removal from Office, and disqualification to hold and enjoy any Office of honor, Trust or Profit under the United States."

In other words, an official impeached by the House and convicted in the Senate is subject to only two penalties: removal from the current office, and a bar against ever again holding that or any other federal office. The Constitution goes on to say that if the conduct for which the official was impeached constituted a crime, he or she could be prosecuted for that crime, but only in a separate proceeding conducted by the regular courts.

There has been fervid speculation in some quarters about whether Trump would voluntarily vacate his office if defeated in an election. In the event of Senate conviction in an impeachment trial, the question would be moot, at least as a constitutional matter. Removal has always been understood to be an automatic consequence of conviction. And the 25th Amendment decrees, "In case of the removal of the President from office or of his death or resignation, the Vice President shall become President." In short, Vice President Mike Pence would become President Pence the moment 67 senatorial votes were officially tallied for any article of impeachment.

The question of whether Trump could nonetheless run for president next year is more complicated. In the impeachment of federal officials, the Senate has adopted the practice of holding a separate vote on the issue of disqualification from future federal office after it votes for conviction. Since at least the 1912 impeachment of Judge Robert Archbald, the Senate has required only a majority vote for disqualification.

If no disqualification vote is held, even a convicted official can re-enter federal service. U.S. District Judge Alcee Hastings was removed from office in 1989 after he was impeached in the House for engaging in a "corrupt conspiracy" — soliciting a $150,000 bribe in a case before him — and convicted in the Senate. But the Senate took no vote on disqualification. In 1992, Hastings ran for and won a seat from Florida in the U.S. House of Representatives, where he remains to this day.

If Trump were convicted by the Senate, but the Senate chose not to hold a disqualification vote, he could in theory run again, win and return to the White House. The path to re-election would also be open if a Senate vote favoring disqualification failed.

Of course, even an impeached, convicted and disqualified Trump could run for re-election, whether as a Republican or as a third-party candidate, in the sense of announcing his candidacy, tweeting madly and holding bellicose rallies. He might even be able to secure a ballot line in some primaries or in the general election. Nonetheless, once disqualified by the Senate, Trump could never legally resume the office of president.

Given the current makeup of the Republican-controlled Senate, Trump's conviction on articles of impeachment is unlikely. But if senators take that step, and don't want to invite even more political chaos than the country has seen over the past three years, they should finish the job and disqualify Trump from ever holding federal office again.

Frank O. Bowman is a professor at the University of Missouri's law school, visiting professor at Georgetown University Law Center and author of "High Crimes and Misdemeanors: A History of Impeachment for the Age of Trump." He wrote this article for the Washington Post.