In the Reagan years, Brock began his career within the neoconservative orbit of The Washington Times. Soon he migrated to The American Spectator, where he became a key figure in the “Arkansas Project,” which was financed by the billionaire Richard Mellon Scaife and was intended to destroy Bill Clinton’s presidency. In addition, Brock assailed Anita Hill, whom he had earlier deemed “a little bit nutty and a little bit slutty,” in a best-selling book. Then, in the late 1990s, he performed a political somersault. In his riveting 2002 memoir, “Blinded by the Right: The Conscience of an Ex-Conservative,” he flayed both himself and his former mentors for toppling into an intellectual and moral cesspool. There the story might have ended. But since then Brock has discovered a new vocation as the founder of Media Matters for America, an organization that seeks to monitor and expose what it sees as conservative misinformation.

In “The Fox Effect,” Brock and his associate Ari Rabin-Havt target Rupert Murdoch’s lucrative flagship cable network, Fox News. They draw on Michael Wolff’s biography of Murdoch as well as on transcripts and leaked memos (some of which Media Matters has already publicized) from Fox journalists and executives to contend that it is not a traditional news organization, but a propaganda outlet intent on reshaping the Republican Party in its own image.

The opening for Fox to make the transition from a right-wing news outlet to a powerful player in the party itself arrived, Brock and Rabin-Havt write, in 2008 with the election of Barack Obama, a presumed radical with an exotic name who didn’t even appear to be a real American. Roger Ailes, the president of Fox News and a former campaign operative for Richard Nixon and George H. W. Bush, “must have been waiting for this moment. . . . Now was his chance to lead a movement — not with his own voice, but, as he had done so effectively in the past, by channeling his political ambitions through others.”

In the first months of Obama’s presidency, Fox reporters and hosts, led by Glenn Beck, steadily misrepresented his aims. The network, the authors say, became “a breeding ground for Republican talking points.” “By denying the president a honeymoon,” they write, “Ailes had set the tone for the rest of Obama’s term.”

They go on to indict Ailes for fomenting the Tea Party movement. Fox News provided what amounted to wall-to-wall coverage of Tea Party gatherings, supporting a Republican campaign vehicle while maintaining the pretense of functioning as an objective news organization. Brock and Rabin-Havt pin much of the blame for the Democrats’ loss in the 2010 midterm elections on Fox, charging that it had “served as the communications hub of the Republican Party” and “used the Tea Parties to build a movement that supplied bodies for the Republican field operation.”

But just how effective has the Fox effect actually been? The network is wildly popular among an older, mostly male conservative cohort, but pushing the movement’s language further to the right has not been an unequivocal political success. Not only was Fox unable to prevent Obama’s election, but it failed to stymie his health care plan. Its record against his re-election campaign in 2012 may well be no better, especially if the economy continues to recover. Yes, Republican stars like Sarah Palin, Rick Santorum, Mike Huckabee and Newt Gingrich are, or have been, on the Fox payroll. But it is Mitt Romney — a Massachusetts moderate who, no matter how much he denies it, laid out the lineaments of Obama’s health care plan — who will quite possibly secure the Republican nomination. Meanwhile, the Tea Party is running out of steam.

What Brock and Rabin-Havt fail to provide is a context. The Democrats did not suffer losses in the 2010 elections primarily because of nasty commentary on Fox; rather, they dithered on health care reform and were repeatedly outmaneuvered by Republican legislators. Nor do the authors explain what would constitute legitimate criticism of Obama: the left’s frustration with the president, after all, mirrors the right’s in viewing him as a detached elitist deaf to the concerns of common folk. At what point is anger against Obama the product of media manipulation, and at what point the result of spontaneous grievances?

Brock and Rabin-Havt also concentrate so closely on the farrago of conspiratorial nonsense spouted by the likes of Beck that they exaggerate its practical significance. The truth is that Beck, who has departed from Fox, will in the future probably be dimly remembered as part of the freak show — the birthers, the allegations of Kenyan socialism in the White House, and so on — that accompanied Obama’s presidency. If anything, such volatile rhetoric has boomeranged: toward the end of their book, Brock and Rabin-Havt themselves state that “ironically, Ailes’s quest to divide has also damaged the Republican Party” by tarnishing more moderate conservatives. For all the authors’ ­apprehension about the network’s influence, this close study of the Fox universe demonstrates not its reach but the limits of conservative jihadism, something Brock should be more familiar with than anyone else.