Many of the words Senator Bernie Sanders used in Brooklyn on Saturday as he kicked off his second run for president were familiar: “revolution,” “economic justice,” “prison-industrial complex.”

But one word was not: “I.”

“I was born literally a few miles away from here,” he told the crowd.

“I lived in a three-and-a-half-room rent-controlled apartment,” he thundered.

“I was educated proudly in high-quality public schools,” he said.

During his last presidential campaign, and throughout his political career, Mr. Sanders has offered a policy-focused message almost entirely devoid of personal details. At Saturday’s rally, however, he did something new: He talked about himself.

“I know where I came from!” he shouted as his supporters roared. “And that is something I will never forget.”