Donald Trump’s loose talk of imprisoning Clinton and his preemptive rejection of the election’s outcome pose one of the most serious challenges to U.S. democracy in recent memory. They endanger the “democratic bargain,” to quote the authors of Losers’ Consent: Elections and Democratic Legitimacy. That study examines how losing works in democracies around the globe, and the bargain at issue “calls for winners who are willing to ensure that losers are not too unhappy and for losers, in exchange, to extend their consent to the winners’ right to rule.” This bargain is also one of the core components of democracy.

On Friday, one of the authors of the study, the political scientist Shaun Bowler, applied his team’s findings to Trump’s warnings about a rigged election. “[G]raceful concessions by losing candidates constitute a sort of glue that holds the polity together, providing a cohesion that is lacking in less-well-established democracies,” Bowler wrote in Vox. Public-opinion surveys from around the world, he noted, indicate that winners and losers interpret the outcome of elections differently. Supporters of losing candidates tend to lose faith in democracy and democratic institutions, even after elections that aren’t particularly contentious. When your preferred politician or party loses, in other words, resentment is inevitable.

This is why the democratic bargain is so important: Winners do not suppress losers, which means losers can hope to be winners in the future. As a result, the losers’ doubts about the legitimacy of the political system gradually recede as they prepare for the next election.

But if the losing candidate doesn’t uphold his or her side of the bargain by recognizing the winner’s right to rule, that acute loss of faith in democracy among the candidate’s supporters can become chronic, potentially devolving into civil disobedience, political violence, and a crisis of democratic legitimacy. How the loser responds is especially critical because losers naturally have the most grievances about the election.

“[I]n the aftermath of a loss, there is plenty of kindling for irresponsible politicians to set fire to,” Bowler notes. “Most politicians who lose elections recognize this potential for mischief, and so they ordinarily make a creditable run at helping to keep matters calm.”

All losing presidential candidates in modern U.S. history have avoided the temptation to fan the flames of grievance, and have instead shown restraint and respect for the peaceful transfer of power. Many Americans take this norm for granted, and it can operate in subtle ways.

In December 2000, for example, Al Gore conceded defeat to George W. Bush after one of the country’s closest and most divisive elections. The Supreme Court halted the recount of votes in Florida and effectively handed the presidency to Bush, even though Gore won the national popular vote and had good reason to argue that the court’s decision was politically motivated.