Cronkite’s coverage of the 1964 Republican convention was judged so verbose and lackluster that the CBS chairman William Paley yanked him. The veteran Robert Trout and a young Roger Mudd were brought in to co-anchor the Democratic convention.

By the 1968 Chicago conventions, however, Cronkite was riding high again. “The Evening News” was tops in the ratings, its anchorman sure of his position and his material. His “Report From Vietnam” had won him widespread respect, and he was at his best as he held the peace as the convention devolved into violence. I remember Cronkite ending one late-night session bidding viewers to “get some sleep,” telling us he’d “see us in the morning.” It was gavel-to-gavel coverage, and he knew we were staying with him.

But Brinkley also reveals Cronkite’s darker, competitive side. He was churlish to colleagues and hated sharing the spotlight. He was so outraged to be co-­anchoring the 1960 convention with Edward R. Murrow that he locked himself in the anchor booth and refused to come out for photos. When Barbara Walters was paired with Harry Reasoner to anchor at ABC, Cronkite was publicly polite, but according to Brinkley, he “privately hoped she’d fail.” This was not news to her. “Let’s just say Uncle Walter wasn’t Uncle Walter to me,” she said. Tom Brokaw agreed: “He was very protective of his seat of power. This nicest-guy-in-the-world was more Darwinian than you could imagine when it came to being top dog.” Cronkite’s ruthlessness was never more in evidence than during the 1952 Chicago conventions. Competition for coverage was fierce, and Cronkite (with the approval of CBS) had the Republican credentials committee room bugged.

Cronkite didn’t want to lose. Nor did he like the idea of giving up the anchor desk, even to Dan Rather, his preferred successor. His last night anchoring “The CBS Evening News” was March 6, 1981, but he was not prepared for retirement. “He had quit too soon,” Brinkley writes. “He had never felt more hopeless. He had a partial interest in everything, without a sharp sense of mission about any one thing.”

It’s time for the elephant in the room. Was Cronkite a liberal?

The left-leaning was right there, Brink­ley notes, for all to hear if not see: Cronkite was always more outspoken off camera. “I thought that some day the roof was going to fall in,” Cronkite said. “Somebody was going to write a big piece in the newspaper or something. I don’t know why to this day I got away with it.” At a dinner honoring the Texas representative Barbara Jordan, he said of the Democratic losses in the 1988 election:

“Liberalism isn’t dead in this country. It isn’t even comatose. It simply is suffering a severe case of acute laryngitis. It simply has temporarily — we hope — lost its voice. . . . But God Almighty, God Almighty, we’ve got to shout these truths in which we believe from the rooftops, like that scene in the movie ‘Network.’ We’ve got to throw open our windows and shout these truths to the streets and to the ­heavens.”

It was “Cronkite’s political coming-out party,” Brinkley writes. “The charade of being Mr. Center was over.” Curiously Cronkite’s liberal bent didn’t detract from his credibility or popularity. It seemed to me that conservatives watched him with great respect, distilling out whatever leftish sentiment they might detect.

But “Cronkite” will endure not for what it tells us about broadcast media but for what it reveals about the man — his paradoxes, his penchant for pranks and dirty jokes, his long and happy marriage.