After writing, co-authoring and editing 42 books on Abraham Lincoln, Harold Holzer is easing back a bit from his day job as senior vice president of external affairs at the Metropolitan Museum of Art — in order to devote more time to Lincoln. A Lincoln painting from life looks over his shoulder at the museum, where he runs the communications shop and seems bemused when a visitor asks what could possibly be left to write about Lincoln.

“I thought the demand and public interest would peak in 2009 at Lincoln’s 200th birthday, but everybody sort of recalibrated,” he says. “Endless events, symposia; it’s unbelievable. Part of Lincoln’s resurgence is how the presidents of both parties have thoroughly embraced him. All the Lincoln boats are floating higher. But don’t try to overanalyze it. I just give reverential daily thanks for vampire killers, Spielberg, Doris Kearns Goodwin and all the rest.”...

Holzer books have been well received by fellow historians. He admires historians like Richard Norton Smith, who also held demanding day jobs while writing distinguished biographies. But his gut inspiration is Howard Dietz, who ran public relations for MGM in Hollywood but, like Mr. Holzer, had a spare-time passion for writing — in Mr. Dietz’s case, brilliant song lyrics, including “Dancing in the Dark.”

One of Mr. Holzer’s proudest moments was the publication, in Polish, of a book he edited with Mario Cuomo called “Lincoln on Democracy.” When Polish Solidarity union workers visited Governor Cuomo in Albany, they told him and Mr. Holzer, then an aide to the governor, that Communism had stripped their nation’s bookshelves of true political history. They pleaded: “Give us Lincoln!,” according to Mr. Holzer, and he and the governor obliged. He reverently points out that the translation of the Gettysburg Address for the book was by Czeslaw Milosz, the Nobel laureate.

His current project about Lincoln and the press is meat and potatoes for Mr. Holzer, who worked media for such New York politicians as Bella Abzug and Mr. Cuomo. “I just love it,” he says, plumbing research on how readers relied on the press to be institutionally, excitingly biased in the 1860s....