It was Donald J. Trump’s best chance to escape his own caricature.
He did not.
After 40 years in the public eye, Mr. Trump decided on Thursday night that he was not interested in revealing himself to America with disarming tales of his upbringing, hard-earned lessons from his tumultuous career or the inner struggles masked by his outward pomposity.
In the most consequential speech of his life, delivered 401 days into his improbable run for the White House, Mr. Trump sounded much like the man who had started it with an escalator ride in the lobby of Trump Tower: He conjured up chaos and promised overnight solutions.
It was a speech that might be remembered, ultimately, as much for what it lacked as for what it contained — and for the message those absences seemed to convey: He is content with the angry voters he has won, who thunderously cheered him on here, and indifferent about wooing those he has not.
For those grasping for new signs of humility, generosity and depth, Mr. Trump offered the thinnest of reeds.
Inside the Quicken Loans Arena, a thicket of American flags behind him, he portrayed himself, over and over, as an almost messianic figure prepared to rescue the country from the ills of urban crime, illegal immigration and global terrorism.
“I alone,” he said, “can fix it.”
But Mr. Trump made no real case for his qualifications to lead the world’s largest economy and strongest military. He is, he said, a very successful man who knows how to make it all better.
Campaign speechwriters from both parties were stupefied.
“It’s a lost opportunity,” said Matt Latimer, who wrote speeches for President George W. Bush. He said he had expected Mr. Trump to plumb his personal life and career for the kind of anecdotes that would turn him, in the eyes of his doubters, from a cartoon into a flesh-and-blood human being.
“A little humanity and self-reflection,” Mr. Latimer said, “is usually very powerful in a speech.”
But Mr. Trump, even at 70, seems constitutionally incapable of, or stubbornly averse to, capturing and conveying the complexities of his existence.