Donald Trump ascended the dais on Thursday night as the most improbable of Republican presidential nominees.

What historical shift, what tremors in American culture, yielded up Mr. Trump’s moment from the depths of the national id? How did a braggadocious Manhattan billionaire with a history of dodgy business deals convince 13 million people feeling battered by a changing world that he is their solution? Chutzpah, reality TV and a hyperactive Twitter account are part of the answer. But Mr. Trump’s nomination is also a referendum on the Republican Party, delivered by working people fed up with leaders who want their votes but don’t address their struggles.

Given a chance to replace the empty sloganeering and self-aggrandizement of his primary campaign with solid proposals worthy of Americans’ trust, Mr. Trump made clear that he instead intends to terrify voters into supporting him, who will protect them from violence, a word that occurs over and over in his remarks.

Asserting that his nomination comes at a moment of national crisis, of “poverty and violence at home, war and destruction abroad,” Mr. Trump offered no solutions beyond his messianic portrayal of himself. “Every day I wake up determined to deliver a better life for the people all across this nation that have been neglected, ignored, and abandoned,” he says in advance excerpts from his speech.