While Hannity alone may not prevent Trump’s impeachment, he’s Fox News’ top-rated host and a major force in a conservative media ecosystem that reflexively defends the president’s actions, rips news outlets, lobs accusations against Democrats, and, at times, fuels “deep state” conspiracy theories and promotes debunked stories. Some Fox hosts and guests have even warned of a “coup,” extreme rhetoric that has been embraced by the president.

But as Fox vows to cover impeachment in a rigorous and fair-minded way in its news programming, if not opinion shows, the network is becoming a kind of Rorschach test for cracks in the president’s media firewall. The calculus is simple: If Fox starts allowing more anti-Trump conservatives to voice concerns about the president’s behavior, it clears the way for conservative House members and senators to express doubts of their own without having to worry about a conservative media backlash.

Joe Walsh, a former Republican congressman and radio host now running a long-shot primary bid against Trump, told POLITICO that current members look to Fox News for signs of what’s acceptable conservative dialogue.

“They don’t fear Trump. They fear his voters,” Walsh said. “They know his voters digest Fox News every day, so they toe the line with what Fox News is doing [and] put out crap about the ‘deep state’ and all this other stuff they really don’t believe in.”