He also expressed bafflement at the strategy of Marco Rubio’s campaign, which held that the candidate could survive a long war of attrition by not losing badly in the early contests. “History shows it doesn’t matter who comes in second, third or fourth,” Stevens said. “You have to win states. It’s like the prison movies where you go find the bull of the yard and punch him out. That’s the only way you become top dog. It turns out that only one candidate has been focused on winning, and that’s Donald Trump.”

Stevens himself endured considerable criticism — from Trump, among others — for the manner in which the Romney general-election campaign was waged. And, like virtually every other commentator, he failed to forecast Trump’s staying power, predicting after the front-runner’s loss in Iowa that he would not win a single primary. But Stevens worked for the two successful presidential campaigns of George W. Bush; his misjudgments have not been the product of inexperience.

The same could be said for the 2016 roster of errant strategists. Todd Harris, who helped Rubio win election to the Senate in 2010 and is now one of his chief advisers, also ran Joni Ernst’s successful Senate race in Iowa in 2014. Cruz’s campaign manager, Jeff Roe, was previously the senior strategist for David Dewhurst, the establishment Republican candidate whom Cruz beat in the 2012 Senate race in Texas. Roe and Harris understand better than most what it takes to appeal to conservative voters. Understanding how Trump could so radically rewrite the campaign playbook is another matter.

“When you work for a serious person, you can’t go out and say things that are just untrue,” said Danny Diaz, Jeb Bush’s campaign manager. “You can’t go out and say things that completely contradict your body of work and record. And Trump feels completely uninhibited making arguments with no foundation in truth. And if you’re a serious candidate, you offer policy proposals. He is operating under different rules, through sheer force of his persona and the celebrity culture he’s taken advantage of. And look, from the perspective of marketing and branding, he deserves a lot of credit.”

Trump clearly benefited from early low expectations, from the news media’s fascination with his outrageous utterances and from an unusually crowded field of candidates. (“Ten candidates on a debate stage — the person who benefited the most was the guy who could say five crazy things to lock in his 30 percent,” Diaz said.) But he also enjoyed the unique status of being a businessman whose only relationship with politics was his boastful assertion that he had been able to game the system in his favor. “At the end of the day, he’s doing really well because he’s not a politician, and everyone else is,” said Mike DuHaime, the senior strategist for Chris Christie. “Others tried to say they were outsiders. He truly was.”