President Donald Trump’s rejection of an orderly transfer of power to Joe Biden, accompanied now by his refusal to concede defeat based on fabricated allegations of electoral fraud, poses a profound threat to American democracy—the most profound yet of his dangerous presidency. That the Republican leadership has supported him in his subversion severely worsens the situation, with dire implications for the future of American politics.

It is unprecedented for an unsuccessful incumbent President and his leading congressional allies to refuse to acknowledge the results of an election. Since 1800-01—the first time the country experienced anything like a transfer of power from one party to another—defeated presidents have bowed to the will of the people. They have not always done so happily. After his loss in 1800, John Adams wrote bitterly that “we have no Americans in America,” and that “a group of foreign liars, encouraged by a few ambitious native gentlemen have discomfited the education, the talents, the virtues, and the property of the country.” Adams was so disgusted that he refused to attend the inauguration of his successor, Thomas Jefferson. But Adams accepted that, as he wrote, “we federalists” had been “completely and totally routed and defeated.”

In 1828, Adams’s son, John Quincy Adams, was depressed by his loss to Andrew Jackson after a savage campaign on both sides, although he had foreseen the outcome for some time. Like his father, Adams failed to show up for his successor’s inauguration, and a few years later protested when the Harvard Board of Overseers voted to present President Jackson with an honorary degree. (Himself a member of the Board, Adams boycotted that ceremony as well, dejected that “my darling Harvard” would honor “a barbarian who could hardly spell his own name.”) In 1869, the impeached and discredited Andrew Johnson, having been passed over for re-nomination, skipped the inauguration of Ulysses S. Grant.

But personal bitterness is one thing; disloyalty to democracy another. Until now, no defeated President has failed to respect the transfer of power, let alone deny the results of the election. There have been two hotly disputed elections, in 1876 and 2000, which produced prolonged wrangling over who won. But even then, once the winner was determined, the loser—first Samuel Tilden, then Al Gore—gave way.

Even on the verge of the Civil War, respect for democracy overcame nasty divisions. Incumbent James Buchanan was not a candidate in 1860, but he strongly opposed the antislavery politics of the new president, Abraham Lincoln, whose election prompted South Carolina and several other Southern states to declare their secession from the Union. Yet Buchanan rode in a carriage with Lincoln to the Capitol from the Willard Hotel near the White House. There, Chief Justice Roger B. Taney, whose opinion in the Dred Scott decision in 1857 had effectively declared the platform of the Republican Party unconstitutional, duly administered to Lincoln the oath of office. At the nation’s hour of maximum peril, the defeated acknowledged their defeat—except, of course, the Confederate secessionists who were posing the peril and who would dissolve the Union rather than submit to democracy.

Trump’s denial of the legitimacy of Biden’s election is a renunciation not just of American tradition but of the remaining chords of comity that are fundamental to American democracy. Urging his tens of millions of supporters as well as his congressional backers to reject Biden’s victory creates not simply a fissure but a chasm in the nation’s politics and government. It is one thing for a loser to criticize the new administration, hoping to turn public opinion against those who vanquished him. Herbert Hoover, after a brief decent interval following his defeat in 1932, became an implacable foe of Franklin D. Roosevelt’s policies, delivering one speech after another attacking the Administration, some of which he collected, four years later, as a book entitled American Ideals Versus the New Deal. Failed presidents may always try to regain the office. Martin Van Buren, an incumbent defeated in 1840, ran again on the third-party Free Soil Party ticket eight years later. Grover Cleveland, beaten in 1888, won the next time in 1892. But for Trump to deny Biden’s legitimacy moves beyond opposition into active betrayal of the constitutional compact, something closer to the Confederate secession, attempting to trash not only the new president but also the democratic process that elected him.

In the short run, of course, the Republican Party could shut down Trump’s assault by disowning it and acknowledging the new Administration as duly elected. Then it could perform as the loyal opposition. But its leaders, Senate Majority Leader Mitch McConnell and House Minority Leader Kevin McCarthy, have supported the MAGA fantasy that Trump may well be the victim of a monumental fraud, if only it could be revealed. The damage the Republican leaders have already done to our democracy through their collaboration with Trump is incalculable. But their test today is far greater than whether they once again humor Trump’s reckless delusions for their own cynical ends, starting with winning the Senate runoff elections in Georgia. The larger question is whether the Republican Party wishes to remain a legitimate democratic political party. McConnell and McCarthy have already given their answers. If they and their respective caucuses persist, they will have tainted their party far beyond what Trump already has.