Of the many troubling things that Republican candidate Donald Trump has said during this U.S. presidential election campaign, the most worrisome may be his claim that the November vote will be "rigged" and that he might not accept the results when polls close. At the first presidential debate last month, the moderator had to twice ask Trump before he said that he would accept the outcome if defeated by Democratic Party nominee Hillary Clinton. Four days after the debate, he reversed himself, saying instead, "We're going to have to see what happens."

It is hard to imagine a statement more corrosive for U.S. democracy. The authority of the president ultimately rests on his (or her) legitimacy as the winner accepted by all electors, even those that did not vote for him (or her). A loser, and especially one who has decried a political system that systematically disenfranchises significant parts of the public, who refuses to accept that verdict undermines the very foundation of the American political system and the individuals who exercise power through it. This disrespect for the democratic process is the most dangerous element of the Trump candidacy.

There have been four U.S. presidential elections when the loser could claim that the results did not truly reflect the will of the people. In 1824, 1876, 1888 and in 2000 the eventual victor did not win a majority of the votes cast. Instead, they won because they amassed the electoral votes needed to claim the White House. And, most significantly, even when the results literally were hanging in the balance, as in Florida in 2000, Vice President Al Gore accepted defeat precisely because he understood the stakes and recognized that the country's future depended on acceptance of the legitimacy and finality of the electoral process by winner and loser alike.