Donald Trump visits "FOX and Friends" in 2011. (Photo by Slaven Vlasic/Getty Images)

“There’s a saying in politics that personnel is policy,” Matt Gertz, a senior fellow at Media Matters, said on a recent afternoon. “The people who surround principals in the political world can have a lot of influence.” Gertz, thirty-four and petite in a suit jacket, is best known for tracking Donald Trump’s Twitter account for clues about his well-reported habit of watching Fox News.

On Twitter and via a Media Matters video archive, Gertz flags when Trump’s posts seem tied directly to programming—on Fox & Friends, Hannity, and Lou Dobbs Tonight. “You can see him bringing in information from these particular programs and then sending out public communications into the world, making particular decisions based on that information.” Trump’s most valuable personnel, Gertz has observed, are the ones Trump sees on TV. “I think what we’re seeing,” he said, “is how the president can be influenced in real time—and the consequences that can have.”

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Gertz has been tracking Trump since the beginning of his presidency, but only began his dive into the president’s Twitter habits in October 2017. He’s had to adapt his life to Trump’s TV watching habits. He gets into the office around 7:30 am, to get a jump on the president’s predictable morning tweetstorms. “I moved my entire schedule forward,” he said. “Generally his daily schedule doesn’t start until 11 when he has his daily briefing, so before that it’s ‘executive time’ when he’s watching television and tweeting about it.” (“Executive time” consists, basically, of the president’s unstructured hours—last week, when Axios released copies of Trump’s daily schedules, it was found to constitute 60 percent of his workday.)

Gertz has observed that Trump’s Fox live-tweeting is less frequent during the middle of the day, when he is more likely to be in meetings (though it still happens). Fox live-tweets tend to surge on holidays and weekends, when Trump is in the residence of the White House or at his golf club in New Jersey or at Mar-a-Lago, in Florida.

“I have an eight-month old,” Gertz told me. “Sometimes the baby is taking a nap and then I can look back and say, ‘Oh wow, the president has done like six tweets this morning, let’s pull up the video archive and see what’s going on here.”

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Gertz’s attention to detail follows Trump’s Twitter behavior down to the moment. For example, Gertz pointed to Philip Bump’s reporting in The Washington Post that Trump takes six minutes on average to send a tweet. (Tweets with videos or images, he believes, based on accumulated White House reporting, are likely sent by a Trump staffer, not by the president himself.) When there’s a big gap in time between tweets that exceeds the time between relevant Fox segments, Gertz can only speculate about what’s going on—and it can get personal. On the day we met, Gertz guessed about one such break: “I think he paused and maybe took a shower or something?”

There were other clues to follow. Trump had started that day by tweeting, “A great new book out, ‘Game of Thorns’ by Doug Wead, Presidential Historian and best selling author. The book covers the campaign of 2016, and what could be more exciting than that?”

Gertz was skeptical. Aside from the fact that the book wasn’t so new (it came out in 2017), the name drop, he said, “was a pretty good tell that it was something coming from Fox & Friends, because the president doesn’t really read books.” Other giveaways to which Gertz has become alert: statistics or figures, an obscure source (who, it turns out, may also have been a Fox guest), topics of little relevance to the news cycle. “If it’s about something hyper specific and weird that no one else is talking about, chances are it’s coming from Fox,” he said.

The impact of Gertz’s analysis may lie in its immediacy—following him on Twitter is like following an annotated Trump—but his accumulated knowledge of Fox programming and its impact on the president has allowed him to make arguments and predictions about Fox’s long-range impact. He had been forecasting a “Fox News shutdown” since as early as last March, by observing a “tug of war” between right-wing media, whose presenters wanted Trump to use a government shutdown to extract concessions on immigration policy, and Congressional Republicans, who would have preferred that he not.

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Fox knows that Trump is watching, and the network steers coverage to speak to him directly. By December, Fox’s “infotainers,” as Gertz likes to call them, won out, and urged the president to “stay strong,” feeding him cherry-picked poll stats that showed he was “winning” the shutdown. Today, Gertz feels confident that Trump will declare a national emergency to build his border wall, because that’s what Fox has been repeatedly telling him to do.

When discussing Trump, Gertz’s tone can be sarcastic, veering on snide. Other times it’s outraged. He told me that this comes from deep concern. “The president of the United States—with access to any expert he wants, all of the information that the federal government has—frequently begins his day by watching this nonsensical propagandistic show about how great he is and then tweeting about its segments in real time,” he said. “Then he goes to work as president and then finishes and watches the nightly Fox News lineup and tweets about that in real time. This is very bizarre. And I think unhealthy.”

Choosing Fox over the public is bad governance, Gertz added, since he’s answering not to the American people, ultimately, but to a news channel that has dubious fact-checking standards. Late last month, before the president acceded to demands that ended the shutdown, Trump worried how the pundits would respond: “The White House reporting on this is that the president is worrying about losing Ann Coulter and Sean Hannity,” Gertz told me. “I mean, if that’s your goal, to placate people whose incentive structure is to be as implacable as possible, you’re not actually going to be able to negotiate with Democrats.”

Gertz figures he’s doing his part to hold Trump accountable for the Fox News feedback loop—and to show how eagerly other outlets pick up the story of whatever Trump posts. “I think it has value, in knowing why the president is saying the things that he says and sometimes doing the things that he does,” Gertz told me. “I think certainly the president’s Twitter habits will be part of the story of his administration,” he added. “And it’s all out there if you look for it.”

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Anna Altman is a writer and editor in Washington, DC.