The role of President Donald Trump’s ominous warnings about the caravan of migrants headed toward the U.S. border from Central America in inspiring the virulent anti-Semite who killed 11 people at a Pittsburgh synagogue on Saturday highlights the destructive consequences of Fox News’ grip on the president.

While Robert D. Bowers, the man accused of carrying out the mass shooting, had criticized Trump for being insufficiently anti-Semitic, critics pointed out that president had “stoked the fears of the Bowerses among us,” deploying incendiary and false rhetoric about the migrant caravan in hopes of bolstering the Republican Party’s standing. “The shooter might have found a different reason to act on a different day,” Adam Serwer wrote for The Atlantic. “But he chose to act on Saturday, and he apparently chose to act in response to a political fiction that the president himself chose to spread and that his followers chose to amplify.”

Trump, in turn, came into contact with that fiction via Fox’s fearmongering. The president’s first public statements about the caravan came in response to a segment he watched on the Fox News morning show ”Fox & Friends,” and in the weeks that followed, his rhetoric and that of the conservative network escalated at pace.

For more than a year, I’ve been studying the Trump-Fox feedback loop, my term for the way Fox News at times is able to set the national media agenda because the president watches the network’s programming, tweets about it in real time and adopts its particular fixations. As the rest of the press scrambles to cover Trump’s comments, Fox’s right-wing obsessions consume the news cycle, whether or not they were originally newsworthy. In this case, Fox News urged him to whip his followers into a frenzy over the caravan, and he did it. There’s no indication that either Fox News or Donald Trump will cut off this campaign of fear.

The caravan formed in Honduras on Friday, Oct. 12. By Oct. 15, it was already receiving substantial coverage on Fox News. The next morning, in response to a report on ”Fox & Friends,” Trump issued his first public statement on the migrants, warning the Honduran government that he would cut its aid if the caravan was not stopped. Trump’s comment generated more coverage both on Fox News and at other media outlets. On Wednesday night, Oct. 17, former House Speaker Newt Gingrich appeared on Fox News and urged Republicans to make the caravan a key voting issue, claiming that “the left is eager” for the caravan to enter the United States.

The next morning, “Fox & Friends” repeatedly aired Gingrich’s comments and suggested that Republicans should take his advice. In response, Trump issued a series of tweets using the caravan’s advance to attack Democrats, saying they had “led (because they want Open Borders and existing weak laws)” an “assault on our country.”

The network and its most powerful viewer spent the next week raising the temperature, stoking fears about whether the migrants were criminals or terrorists, calling the caravan an “invasion” and describing its approach as a national emergency. Escalation bred response bred further escalation, with no sign of a line beyond which the president and his propagandists wouldn’t go.

I’ve written before of the perils of having a president who relies on conservative cable news hosts to help him understand current events. When federal policy and personnel shifts can be driven by a Fox-inspired presidential whim, the network’s influence is staggering. The greatest risk is that Trump could use his unilateral control of the U.S. nuclear arsenal in response to a Fox segment; Trump was reportedly unnerved by b-roll the network aired in March 2017 of a North Korean missile launch, convinced that it was happening live. But on a day-to-day basis, the major concern is that the president is a demagogue who constantly lashes out at his perceived enemies in order to secure his base’s support, and Fox News’ programming is providing him with targets for his ire, whether that’s protesting NFL players or recalcitrant Justice Department officials. That pattern has played out again and again since Trump ascended to the presidency.

“Ordinarily,” Serwer wrote, “a politician cannot be held responsible for the actions of a deranged follower.” So, too, it usually doesn’t make sense to attribute a president’s actions to a news network. But Trump is suggestible, he watches Fox News constantly, and the network’s commentators are aware of that. In lighter moments, the “Fox & Friends” hosts joke about the president’s tendency to watch the programs. In heavier ones, the program’s commentators openly offer him advice, telling him not to sit down with special counsel Robert Mueller or pull troops out of Syria.

But on the Monday after the synagogue murders, nothing had changed. The migrants were again drawing coverage on “Fox & Friends” (“Border Battle Rages as Caravan Heads to U.S.,” read one chyron). And hours later, Trump tweeted that the migrants were conducting “an invasion of our Country.”