“We need the truth,” Mr. DeLemus went on. “We don’t have to like the truth. But we need it.”

The adulation that Mr. Trump is enjoying now can be a complicated, paradoxical gift. Voters like Mr. DeLemus, who said he tended to vote Republican and identified with the Tea Party movement, often draw motivation from outsize personalities like Mr. Trump. But they have also generally rejected any singular figure as a leader. And in that sense, Mr. Trump could find his moment fleeting, the latest showman to lead a movement that has so far refused to be led.

Mr. Trump has found success by putting a sharper edge on a popular conservative message: that the United States is an exceptional nation run by unexceptional people who are fundamentally altering what it means to be American.

In Las Vegas, he lamented: “We don’t have victories anymore. We used to have victories. We used to be great.”

In Phoenix, he said: “We have stupid leaders. The American dream is dead. But I’m going to make it bigger, better and stronger.” To chants of “U.S.A.! U.S.A.! U.S.A.!” he vowed: “Don’t worry, we’ll take our country back. Very soon.”

The implication is that he will take the country back from incompetent leaders and undocumented immigrants. And this is where there is a darker side to his promises to make America great again, one that many critics, including Republicans, say feeds on xenophobia and racist caricatures of immigrants.