Alan did not escape journalism entirely. He became a singularly public kind of historian, someone who reached out beyond his academic scholarship and engaged with the world at large through the media in an accessible style.

Nancy Weiss Malkiel, a historian and later dean at Princeton who was Mr. Brinkley’s adviser on his senior thesis, said he had written with a grace and flair unusual for an undergraduate.

“Even then, he had an uncanny feel for language — a sense of pace, style, composition and felicitous phrasing all too rare among historians in general, let alone history students,” she wrote in the tribute book.

Mr. Brinkley wrote his senior thesis on the Louisiana politician Huey P. Long. He once described the thrill he felt doing research with primary documents.

“I’ll never forget the feeling of opening, for the first time, a box of papers, and holding in my hand a letter that Franklin Roosevelt had written and signed,” he wrote after his first trip to the Roosevelt Library in Hyde Park, N.Y.

Touching that letter, he added, gave him “the sense of being a part of the great tradition of historians who have built their work around this exposure to the immediate product of the minds of the great figures, and not so great figures, of our history.”

His senior thesis became his Harvard dissertation and, later, his first book, “Voices of Protest.” He was fascinated by how both Long and the Rev. Charles E. Coughlin, the chief subjects of that book, had used the radio in the 1930s to mobilize their supporters.