But the change of season from summer to fall typically brings a reckoning for presidential candidates. Campaigns begin spending heavily on advertising, promoting their candidates and attacking rivals.

Voters think about candidates more rigorously. When fall turns to winter, the contests to actually select presidential nominees begin. The accelerating gauntlet of televised debates — for Republicans the next one is Oct. 28 on CNBC — offers a ready guide to their performance under pressure, face-to-face.

That will test Trump’s staying power in several ways. His lead in some polls has eroded somewhat in the wake of media scrutiny and attacks from rivals, on debate stages and off. If that continues, he’ll have to decide whether the “free media” of news coverage can keep him afloat or he’ll be forced to begin writing the sort of large advertising checks he hasn’t needed so far.

At the same time, he’ll have to decide how much of the campaign grind he wants to tolerate. Hearing cheers from large crowds attracted by a political novelty may be thrilling; trudging through snow and ice in Iowa and New Hampshire waging hand-to-hand combat for votes may not be. Trump’s calling card is his reputation for winning. Politicians who make it to the White House usually must demonstrate a stomach for losing before they get there.

That made Trump’s reflections on his prospects this week especially intriguing. I asked whether he’d exit the race if he were no longer, in the phrase he likes so much, “leading every poll.”

“Well, I’m not a masochist,” he said. “If I fell behind badly, I would certainly get out. I’m in this for the long haul,” Trump concluded. “That doesn’t mean someday I don’t wake up and I say, ‘Wow, I’m really tanking.’ Well, if I tank, sure, I go back to the business. Why wouldn’t I?”