Abraham Lincoln has been portrayed in many roles — as emancipator, politician, military leader, orator, self-made man and others — but his canny manipulation of the popular press has received little attention. Harold Holzer, a prominent authority on America’s 16th president, opens many vistas on this fascinating topic in his new book, “Lincoln and the Power of the Press,” a monumental, richly detailed portrait of the world of 19th-­century journalism and Lincoln’s relation to it. Holzer demonstrates that even as Lincoln juggled many war-related demands, he kept a close eye on American newspapers and tried to influence them however he could.

Lincoln declared that “public sentiment is everything,” and in his era nothing shaped public sentiment more powerfully than journalism. Advances in printing technology and newspaper distribution caused a rapid rise in the number and circulation of American papers. As the lexicographer Noah Webster commented, “In no other country on earth, not even in Great Britain, are newspapers so generally circulated among the body of the people, as in America.” By the eve of the Civil War, America’s 4,000 newspapers and periodicals, more than three-quarters of which were political in nature, had a strong impact on voters.

Newspaper editors were a brazen, contentious lot. Holzer focuses on the so-called Big Three of American journalism — James Gordon Bennett of The New York Herald, Horace Greeley of The New York Tribune and Henry J. Raymond of The New York Times. These editors, Holzer writes, “loved their profession as passionately as they loathed each other, and each believed, in his own way, that he was all but ordained to chart the course for the future of civilization.” The three took different stances on Lincoln and the Civil War. Raymond, a moderate Republican, was the most supportive of Lincoln, while Bennett, a racist Democrat, was the least. Greeley, an important antislavery voice and a promoter of faddish reforms, swung between glowing praise and harsh criticism of the president, even as he battled his rival editors.

The popular press, therefore, was slippery, making Lincoln’s efforts to deal with it immensely challenging. Deal with it he did, in masterly fashion. Sometimes he used his “rustic charm,” as with Raymond, who during the war turned against Lincoln but was won back to the president’s side after a relaxed chat at the White House. At other times, Lincoln wisely backed off from confrontation, as when his fruitless efforts to fight and woo the belligerent Bennett led him to realize that responding publicly to the nation’s leading newspaperman was a losing proposition. With the unpredictable Greeley, Lincoln exhibited patience and tact. When in 1864 Greeley arranged a peace conference at Niagara Falls with Southern representatives, to whom he offered lax terms for ending the war, Lincoln confided to a friend that Greeley was causing him “almost as much trouble as the whole Southern Confederacy.” But instead of interfering with the quixotic editor, Lincoln let him go on his peace mission, knowing it would fail; the Southern agents, it turned out, had no authority to negotiate for the Confederacy, and Greeley’s toothless proposals made him appear craven.