“He’ll never concede anything to the left,” said William Nardi, a college student in Boston, who used to look up to Mr. Shapiro. “He’s saying the left is wrong and I’m right. Kids love that. All they care about is this feeling that they are right and that their identity is preserved. That’s what he gives them.”

Conservatives say he is a force for good. Liberals may not like his conclusions, but they are guiding young people at a time when the conservative movement is adrift and ideas of white nationalism are competing for their attention. Mr. Shapiro, an Orthodox Jew, was one of the first to call out the alt-right movement, denouncing it as racist and anti-Semitic at a time when most people saw it as counterculture and cool. He paid a price. He received 38 percent of all anti-Semitic tweets aimed at journalists in 2016, the largest single share, according to the Anti-Defamation League.

“There’s a real battle for hearts and minds going on right now and Ben is one of the main warriors,” said David French, a columnist for National Review. Mr. French calls Mr. Shapiro a “principled gladiator.” His aggressive tone draws in audiences, he said, but he does not attack unfairly, stoke anger for the sake of it, or mischaracterize his opponents’ positions. He even hits his own side, as he did with Sean Hannity for not weighing in on Roy S. Moore, the embattled Alabama Republican, and Mr. Bannon for supporting him.

“He appeals to the better angels of his audience’s nature, while still being a pugilist, and that’s quite a skill,” Mr. French said.

Mr. Shapiro grew up in Los Angeles in a Jewish family of Reagan Republicans. His parents both worked in Hollywood, his mother as an executive of a TV company and his father as a composer. They lived in a small house, his parents in one bedroom and he and his three sisters in the other. They had political discussions around the dinner table. He was patriotic. He dressed up as John Adams every year for Halloween from the age of 5. He had a favorite musical: 1776.

He is less established than Sean Hannity or Rush Limbaugh, but his audience is younger. And instead of hunkering down in a studio, Mr. Shapiro travels the country, speaking at colleges (he’s been to 37 since early last year) and on panels.