The history of American politics is littered with carnage, but little compares to what’s currently roiling the Republican Party. PHOTOGRAPH BY SCOTT OLSON / GETTY

“The Republicans never do any serious fighting in public,” H. L. Mencken declared in 1932, just before the G.O.P.’s Convention, where Herbert Hoover ran for the nomination, all but unopposed. Less than a month later, it took the Democrats four ballots and five days of sweaty deal-making before F.D.R. won his party’s nomination, defeating the former New York Governor Al Smith with delegates thrown his way by the Texan John Garner. “The Democrats, unlike the Republicans, always do their fighting in public,” Mencken wrote. “The history of the party is one long record of ambushes, treasons and kidnappings.” So, too, is the history of much of American politics. But hardly anything in the history of either party compares to the present carnage in the G.O.P.

And that’s saying something. After all, at the nation’s Cain-and-Abel political founding, Aaron Burr, Thomas Jefferson’s Vice-President, fatally shot Alexander Hamilton, who had been George Washington’s Treasury Secretary. Presidents have famously betrayed their Vice-Presidents; parties have collapsed; voters have come to blows. In 1832, Andrew Jackson dumped Vice-President John C. Calhoun, throwing him under the proverbial stagecoach for Martin Van Buren. In 1854, when the American Party couldn’t agree on a candidate, its dissenters split off into the North American Party. In 1856, two different Missouri delegations showed up at one Democratic Convention and got into a brawl on the floor. Until 1896, not a single Election Day passed in the United States without someone getting killed at the polls.

Democrats really have liked to do their fighting in public. The Democratic mess, for a long time, had to do with Southerners, who bolted from Conventions and nominated their own candidates. When Southern delegates departed the Convention in 1860, the chairman announced, “The delegations of a majority of the states of this Union have, either in whole or in part, in one form or another, ceased to participate in the deliberations of this body.” And, with that, he quit.

Parties have dumped incumbents, which has generally meant losing the election. The Democratic Party refused to nominate the impeachable Andrew Johnson in 1868, allowing Ulysses S. Grant, a Republican, to win the White House. Candidates have fallen apart. Horace Greeley, who ran against Grant in 1872, died before the Electoral College even met. Not infrequently, party stalwarts have despised their nominee: in 1972, the year that George McGovern won the Democratic nomination, “Anybody but McGovern” was a Democratic slogan. (McGovern lost to Richard Nixon; after Watergate, many people pasted bumper stickers to their cars that read, “Don’t Blame Me—I Voted for McGovern.”)

Candidates have done ridiculous things. In 1968, Nixon appeared on “Laugh-In.” Parties have quite often nominated scoundrels. But running for office keeps getting creepier. Presidential elections are run by polling organizations, political consultants, and all manner of hucksters, frauds, and toadies. Political consulting is a six-billion-dollar-a-year industry. Under these circumstances, campaigning itself appears, to most ordinary people, an abandonment of humility, charity, and generosity, in favor of self-promotion, money-raising, and pandering. Barney Frank once said, “Anybody who says he enjoys campaigning is either a liar or a psychopath.”

And then came Donald J. Trump. He leads the Republican Party the way the head of a rebel army holds a capital city. This isn’t an ambush or an act of treason or a kidnapping. This is a siege. He plans to build walls; he promises to put his opponents in prison. He enjoys harems. He admires tyrants. He erects monuments to himself in major cities. He holds entertainments in America’s stadiums, where he toys with his political enemies, delighting his band of followers while terrorizing other citizens. Over the weekend, he insisted that he will neither retreat nor surrender.

Meanwhile, he invokes the people: they, he says, have chosen him, and will elect him; the people love him. Do they? Joe McGinniss once observed that the American voter “defends passionately the illusion that the men he chooses to lead him are of a finer nature than he” and that “it has been traditional that the successful politician honor this illusion.” That tradition has ended. No one in the Republican Party can possibly believe that Trump is a better person, a man of finer nature, than the ordinary American voter. The problem for the Party is that no one, including House Speaker Paul Ryan, can even pretend to believe that anymore. No one can believe that in daylight, or in the darkest hour of night, while Trump, restless, tweets about the conspiracies that he believes are being hatched by his enemies—men and, especially, women—to fell him.