It would be one thing if Ms. Pirro were only spouting off on television. But she is a friend of Mr. Trump’s and has met privately with him and his top advisers to sell her half-cocked theories. After Mr. Trump’s victory last year, she interviewed to be his deputy attorney general, a job that would have empowered her to fire Mr. Mueller on her own.

To put it mildly, this is insane. The primary purpose of Mr. Mueller’s investigation is not to take down Mr. Trump. It’s to protect America’s national security and the integrity of its elections by determining whether a presidential campaign conspired with a foreign adversary to influence the 2016 election — a proposition that grows more plausible every day.

If the president’s supporters are upset about how close that investigation is getting to the Oval Office, they should ask not whether any F.B.I. investigator has ever held an opinion about politics, but rather why Mr. Trump chose as his closest advisers people with a tendency to talk to Russian officials and then fail to tell the truth, again and again, about the nature of those communications. As The Times’s Bret Stephens wrote: “Fire? Maybe not. But we are dying of smoke inhalation.” (Mr. Trump’s defenders might also recall that the president himself prompted Mr. Mueller’s appointment when he fired Mr. Comey, who had been overseeing the Russia investigation.)

When the propagandists say, “Get rid of Mueller,” it’s not the truth they’re trying to protect; it’s Mr. Trump himself. Any genuine interest in objective reality left the building a while ago, replaced by a self-sustaining fantasyland. If it’s hard to understand how roughly three-quarters of Republicans still refuse to accept that Russia interfered in the 2016 election — a fact that is glaringly obvious to everyone else, including the nation’s intelligence community and Mr. Trump’s secretary of state, Rex Tillerson — remember that a majority of the same people continue to believe that President Barack Obama was born in Kenya.

There was a time not too long ago when Republicans in Congress seemed genuinely interested in protecting Mr. Mueller — who, it bears noting, was originally appointed to head the F.B.I. by George W. Bush and who was named special counsel by Deputy Attorney General Rod Rosenstein, also a Bush appointee. But Fox’s alt-reality vortex has sucked in previously levelheaded members of the G.O.P. like Lindsey Graham, the South Carolina senator who said as recently as October that there would be “holy hell to pay” if Mr. Trump tried to fire Mr. Mueller. Last Friday, Mr. Graham tweeted in support of “a Special Counsel to investigate ALL THINGS 2016 — not just Trump and Russia.” On Monday night, according to Axios, Jay Sekulow, one of Mr. Trump’s personal lawyers, called for a special prosecutor to investigate … the special prosecutor. The tipping point? An article on Fox News’s website about a top Justice Department official’s wife and her work for Fusion GPS, the research firm behind the so-called Steele dossier.

None of these attacks or insinuations are grounded in good faith. The anti-Mueller brigade cares not a whit about possible bias in the Justice Department or the F.B.I. It simply wants the investigation shut down out of a fear of what it might reveal. But if your man is really innocent, what’s the worry?