To be fair, it’s not hard to understand why it took the G.O.P. and much of the press so long, too long, to take Donald Trump’s candidacy seriously. Many times before, he flirted with running, and, each time, he quit. His bids were stunts. Still, he learned something from those stunts, and the distance between his earlier bids and this one suggests that, while much in American politics has changed, Trump has not.

“A Trump Presidential Bid?” the New York Times wondered, in July of 1987. At the time, Trump was forty-one, and “believed to be a Republican,” according to Abe Hirschfeld, a Florida businessman who led the effort to draft him into the race in which George H. W. Bush, as Reagan’s Vice-President, was the presumptive G.O.P. nominee. “There is absolutely no plan to run for mayor, governor, or United States senator,” a Trump spokesman said, coyly. “He will not comment about the Presidency.” Meanwhile, Trump had taken out a full-page ad in the Times, the Washington Post, and the Boston Globe, ahead of the New Hampshire primary. “There’s nothing wrong with America’s Foreign Policy that a little backbone can’t cure,” the headline read, above a letter in which Trump complained that Americans were being ripped off by foreign powers.

The real-estate magnate, as the Times delicately noted at the time, had “no particular background in foreign policy.” All things considered, that was a generous, if not entirely accurate, assessment. Three years before, Trump had offered his services as the United States’ chief negotiator with the Soviet Union on nuclear disarmament. “Some people have an ability to negotiate,” Trump told the Washington Post, in 1984. “It’s an art you’re basically born with. You either have it, or you don’t.” Did it matter that he didn’t know anything about nuclear warheads or the capacities of missiles? No, because he could learn so fast you wouldn’t believe it. “It would take an hour-and-a-half to learn everything there is to learn about missiles,” he said. “I think I know most of it anyway.”

Trump never did become a negotiator during the nuclear-arms-limitation talks under the Reagan Administration. But in October, 1987, eyeing the election of 1988, he went so far as to give a stump speech before the Rotary Club of Portsmouth, New Hampshire. He arrived by helicopter and was greeted by “Trump for President” placards. “He’s very exciting,” Judy Taylor, the wife of a former club president, said. “Money is power and power is the ultimate aphrodisiac.” “I’m not here because I’m running for President,” Trump said. “I’m here because I’m tired of our country being kicked around.” He promised to eliminate the budget deficit. He had a plan. He said he’d make countries like Japan, Saudi Arabia, and Kuwait pay it off: “There is a way you can ask them and they will give it, if you have the right person asking.”

The next month, Jim Wright, the Democratic Speaker of the House, asked Trump to serve as the host of the Democratic congressional dinner. Trump declined the invitation but, courted and flattered by Democrats, he put off his (presumptively Republican) Presidential bid, having sold a great many copies of the book he published that year, “The Art of the Deal.”

Twelve years later, in 1999, Trump, fifty-three, was about to publish a new book, “The America We Deserve.” That summer, rumors began to spread about a possible Trump candidacy. “Mr. Trump is trying to determine whether there is a place in American political life for a rogue,” Adam Nagourney reported slyly, in the Times. ...