Your Sunday Night Homework

Historians see in Mr. Trump’s candidacy the winding together of different strains in reactionary politics under a single banner. No reality television star has run for president before, but Mr. Trump, with his grasp of the art of notoriety, has forebears of a kind in General MacArthur and Charles A. Lindbergh, the celebrity aviator whose “America First” slogan Mr. Trump has appropriated, and in Hearst and Henry Ford, a pair of renowned and eccentric tycoons who eyed the presidency.

His message contains echoes of George Wallace, the segregationist Alabama governor who sought the White House on a law-and-order platform, and of Mr. Perot and Lee A. Iacocca, modern industrialists drawn to politics and preoccupied with economic threats from Asia and Latin America.

Viewed from this angle, Mr. Trump looks less like a singular phenomenon of 2016, and more like the political equivalent of a comet that crosses the track of an American presidential campaign every few decades.

“We’ve seen everything in Trump before,” said Kevin Kruse, a political historian at Princeton, “but we’ve never seen it all together at once.”

For much of the 2016 campaign, Mr. Trump has defied ideological labeling: He has ignored traditional cultural wedge issues like abortion rights and same-sex marriage, and has taken shifting and often contradictory stances on a host of other matters, from military intervention in Syria to the concept of universal health care.

Mr. Trump has brusquely dismissed the charge of philosophical inconsistency. “I’m a conservative,” he said in a speech in May in California. “But at this point, who cares?”

Yet beneath his swerving and scattered policy agenda, he has been steadfastly consistent over time on a few broad inclinations that define his political worldview.

To the extent that he has an ideology, it is a kind of fortress conservatism, taking a bunkered outlook on the world and fixating on challenges to America’s economic supremacy and to its character as a nation defined by the white working class.

Patrick J. Buchanan, who ran for president both as a populist Republican and as a third-party immigration hawk, called Mr. Trump a kindred spirit. “You could call it tribalism,” Mr. Buchanan said. “You could call it ethno-nationalism.”

Since Mr. Trump first toyed with running for president in the 1980s, he has been hostile to foreign trade and immigration and suspicious of international organizations he views as impinging on America’s free hand. He is distrustful of alliances with less powerful countries, which he has characterized as freeloading off America’s wealth and power.

In the 2016 campaign, Mr. Trump has suggested withdrawing from NATO and pulling troops back from longstanding bases in countries like South Korea and Germany. His threats are a precise echo of a speech he gave in New Hampshire in 1987, declaring that the United States had been “kicked around” by ungrateful allies in Asia and the Middle East.

In domestic matters, Mr. Trump’s main impulse is toward hard-line law and order. He is indifferent to civil liberties and contemptuous of objections to racial targeting. For decades, he has described the country as harried by rampant crime, and has typically placed blame with different nonwhite communities, including urban blacks, Hispanic immigrants and Native Americans.

Long before he called for banning Muslim immigration and torturing terrorism suspects, Mr. Trump argued for unleashing the New York Police Department to attack social unrest with a mailed fist. He spoke approvingly of the Chinese government’s brutal crackdown in Tiananmen Square. He recently expressed admiration for Vladimir V. Putin, Russia’s autocratic president, and Saddam Hussein, the Iraqi dictator, whom he praised as tough on terrorism.

He is not the first American businessman with presidential aspirations to be drawn to strongman government: Hearst and Ford, the anti-Semitic car manufacturer who considered a presidential bid in 1924, both maintained cordial and even admiring relations with emerging fascist regimes in Italy and Germany.

Charles Murray, a conservative scholar at the American Enterprise Institute, said Mr. Trump’s autocratic tendencies placed him well outside the conservative intellectual mainstream.

“The word fascist is simply thrown around too easily, and so I don’t want to use that word. But part of Trumpism is the man on the white horse,” Mr. Murray said. “That’s neither left nor right. That’s authoritarian, and it’s really, really scary.”