If Donald Trump loses the election and doesn’t concede, it won’t violate the US Constitution. But it would break a tradition of concession that dates back more than a century and has achieved quasi-constitutional status. And like most enduring political customs, its value goes beyond graciousness: It helps ensure the continuity of government and offers a legitimating assist to democracy itself.

It’s a matter of interpretation exactly when the practice of concession began. Thomas Jefferson drafted a letter of concession to John Adams even before the election of 1796 was complete, in which he said he expected to lose and warned Adams to be careful lest Alexander Hamilton cheat him of his “succession by a trick.” In the end, Jefferson didn’t send the letter, but instead gave it to James Madison, who passed on its contents indirectly to Adams.

In 1861, Stephen Douglas, the defeated Democratic nominee, called on Abraham Lincoln to say that “partisan feeling must yield to patriotism.” (Al Gore quoted Douglas in his own concession speech after the Supreme Court ruled in Bush v. Gore that George W. Bush was the winner of the 2000 election.) With the preservation of the union in the balance, Douglas’ comment was especially important -- although as it turned out, woefully insufficient.

The first modern concession required the aid of technology. On Nov. 5, 1896, William Jennings Bryan sent a telegram congratulating William McKinley on winning the election and stating, in the language of a courtroom lawyer, “We have submitted the issue to the American people and their will is law.” McKinley replied by telegram the very next day acknowledging “receipt of your courteous message.”

Al Smith seems to have been the first to broadcast a concession speech -- a nice coincidence given Trump and Hillary Clinton’s joint appearance Thursday night at the Al Smith dinner.

Concessions have three different effects, each valuable in its own way. The first is to reduce uncertainty over succession. This may seem like a minor concern in a stable democracy, but it’s always there under the surface. To see how, think back to 2000, when legal wrangling over a recount in Florida created doubt as to who would be the next president.

In retrospect, the period from election day on Nov. 7 that year to Dec. 14, when the Supreme Court ruled, was actually a remarkably risky one. What if the terrorist attacks on the World Trade Center and Pentagon had happened during that uncertain time instead of 10 months later? President Bill Clinton was not only a lame duck, but one who had narrowly survived impeachment. Decisive action would have been necessary. Ideally in that circumstance, a departing president would consult with an incoming president before committing to a course of action that would have to be managed by the next administration. Yet there was no president-elect.

The worries created by that extreme case are relevant to the delicate phenomenon of ordinary transfers of power. For millennia, most societies relied on some form of hereditary monarchy -- not so much because kings are effective rulers, but because hereditary succession reduces the risk of a failed transition.

Democracy succeeds at transitions only when it’s able to reduce the costs of uncertainty. A concession signals to the public that the transition is going to happen smoothly.

The second effect of a concession is to make the election appear legitimate. No one likes to lose. But by acknowledging that the people have spoken, the loser affirms that the process was basically fair.

Trump seems unwilling to do that, at least in advance. The idea that the “system” is “rigged” entered political parlance this year as a more general critique, voiced in different forms by Vermont Sen. Bernie Sanders as well as by Trump. But Trump now proposes, with little or no evidence, that the actual voting procedures might themselves be literally rigged.

If the public doesn’t believe that voting has been conducted fairly, the outcome can lose legitimacy fast. Belief in the fairness of the voting results is, in fact, linked to an overall faith in the fairness of the system of government, precisely what’s been eroded in this campaign.

Third and finally, concessions say that the losing candidate intends to treat the new government as duly constituted by law. In that sense, it’s a renunciation of open resistance. Douglas was making it clear to the nation that he would not support the secession efforts that were well along by the time of Lincoln’s inauguration.

Thankfully, we’re not on the brink of civil war. But after more than two years of race-related clashes between police and protesters, and occasionally violent incidents at Trump rallies, it’s worth remembering that even limited violence can harm democratic stability and security.

Trump probably wouldn’t start riots by refusing to concede. But it’s not something we should want to find out.

By Noah Feldman

Noah Feldman is a Bloomberg View columnist. He is a professor of constitutional and international law at Harvard University and was a clerk to U.S. Supreme Court Justice David Souter. –Ed.

(Bloomberg)