Great job, Mr. President! Time to retire.

Rarely in American history has it been as clear that the two major parties’ nominations for president are interactive — what one party does is likely to have an impact on what the other party does.

On the Republican side, of course, former President Donald J. Trump has a commanding lead, while President Joe Biden currently has no serious competition among Democrats. The possibility of a three-way race cannot be discounted, especially given Trump’s likely unwillingness to sit idly by and watch if his legal problems topple his effort to reclaim the presidency.

So yes, it’s complicated. This column is one lifelong Democrat’s effort to sort through some of the many imponderables. Doing so leads to a single conclusion: President Biden can take great satisfaction in the many important, positive things he has done in domestic and foreign policy — and the best thing he can now do is to retire after completing his term, allowing a new generation of leaders to take up the Democratic Party’s banner.

Would Biden win if he continues his plan to run again? The answer depends on him, other Democrats, and the Republican Party faithful. If he runs against Trump, there is every reason to expect that Biden would win again, although it could be an Electoral College squeaker. But let’s assume a victory. We would have a president who would be older than any of his predecessors on Inauguration Day, and who would be 86 years old when his successor took the oath. I wish President Biden the best of health, and may he live to 120. But the job of chief executive and commander in chief is too demanding and critical to take unnecessary chances. He is too old to be signing on for another four years. Doing so is irresponsible.

What if something were to happen to Biden between the 2024 Democratic National Convention and Election Day? Or between Election Day and Inauguration Day? Suppose his health (and our luck) holds, but sometime during his second term he suffers a disabling health decline (or worse)? We would have to employ the 25th Amendment, or Vice President Kamala Harris would become president in his place, either temporarily or for good. Has she shown herself capable of leading the country? Worse yet, if she did ascend to the highest office, would she be able to secure the required Senate and House approval of her choice of a successor as vice president?

Suppose, for example, that the GOP continues to hold onto a bare majority in the House of Representatives. Would the House vote for a Democrat as vice president, knowing that the alternative of keeping the position unfilled would place the Republican House Speaker as next in the line of presidential succession? And what if the GOP loses the House but gains a majority in the Senate? Am I the only one who thinks Senator Mitch McConnell (R-Ky.) — he of the Merrick Garland Supreme Court blockade — would be perfectly willing to block Senate approval of a Harris nominee as successor vice president? Or that Sen. Joe Manchin (D-W.Va.) might once again use his leverage to a bad end?

What if Trump is not the 2024 GOP nominee? He might of course try running as a third-party candidate, but it seems likely that doing so would only benefit Biden (or whomever was the Democratic candidate if Biden drops out). But put aside the possibility of a Trump third-party run. How would Biden do against some other Republican nominee? Looking over the current field, none of the Republican hopefuls seems likely to do better against Biden than Trump did in 2020 (when he lost).

And what if, as I hope, Biden opts to retire after one term? Trump, if nominated again, would be a wounded general election candidate, and wouldn’t hold much appeal for the independents and moderate Republican voters he would need to succeed on Election Day. There are several proven vote-getters in the next generation of Democratic officeholders who would beat either Trump or any of the current field of GOP hopefuls. Examples include Minnesota Sen. Amy Klobuchar and the popular governors of Wisconsin, Illinois, California, Maryland and Pennsylvania. Even relatively obscure governors can be attractive presidential candidates (think of Jimmy Carter and Bill Clinton). Nor is there a shortage of impressive Democratic candidates of color who might make up for Vice President Harris’s not getting the brass ring, including Georgia Sen. Raphael Warnock, New York Rep. Hakeem Jeffries, Maryland Gov. Wes Moore and Kansas City Mayor Quinton Lucas. Democrats should not be afraid of a contest for the party’s presidential nominee in 2024.

It is often the case that leaders, including political leaders, find it difficult to turn their tasks over to the next generation. When the position is one that involves great responsibility and yields enormous satisfaction, the respect of one’s fellow citizens and a place in history, the possibility of remaining in office as long as possible must be extraordinarily tempting. After all, no greater honor can be earned in American public life than to serve the constitutionally permitted two terms. Yet, second terms often yield only strife, illness and disappointment (think of Wilson, Nixon, Reagan, Clinton and George W. Bush), while history may prove to be kind indeed to those who serve only a single term (e.g., Ford, who finished out what was to have been Nixon’s second term, and Carter).

President Biden has enjoyed an unusually long and successful career in public life. The best thing — the wisest and most noble thing — he can do now is to clear the way for the next generation of leaders to compete for the office he currently holds. Unlike President Lyndon B. Johnson’s March 31, 1968 announcement that he would not run for a second full term, Biden’s abandoning the quest would be an act of both patriotism and optimism. It would also set the stage for the next Democratic president to be able to serve two terms, thus cementing Biden’s significant legacy much more firmly in place.

Eugene R. Fidell is a senior research scholar at Yale Law School.