Pop quiz: how many branches of government are there in the United States? If you said “Four,” go to the head of the class. As of May 17, 2017, the traditional three branches of  Congress, the Executive, the Judiciary, are joined by the Office of Robert S. Mueller III, Special Counsel in charge of destroying the president.

It’s been a fun year. It’s not everyone, after all, who so thoroughly commands the police power of the state that he can order a predawn, guns-drawn raid on people he doesn’t like. Usually, that drama is reserved for dangerous criminals—terrorists, murders, major drug dealers. But Paul Manafort, a businessman, was close to Donald Trump, so he and his wife got the SWAT-team treatment on suspicion of a white-collar crime.

Just a couple of days ago, a long list of “gotcha” questions that Mr. Mueller wants to pose to President Trump was leaked to the press. “How was the decision made to fire Mr. Flynn on Feb. 13, 2017? What was your reaction to news reports on Jan. 12, 2017, and Feb. 8-9, 2017? What was the purpose of your Jan. 27, 2017, dinner with Mr. Comey, and what was said?”

And on and on. These are what one commentator called “perjury traps,” the sort of thing rogue prosecutors like the horrible Patrick Fitzgerald and Robert Mueller use to entrap innocent people. Ask Scooter Libby, who was just pardoned by the President for a non-existent process crime.

In order to get a job in Washington, you have to memorise and spout the mantra “Robert Mueller is a straight arrow.” Everyone from Trey Gowdy on down keeps saying that. I used to believe it, or at least half believe it. Mueller was supposed to be above reproach, incorruptible, a man of duty (or, to alter James Comey’s phrase, “a higher duty”).

In fact, Robert Mueller is a fanatic, one of those gleaming-eyed ascetics who always pop up when a secret police gets going. He should take a page from Talleyrand and say to himself in the mirror every morning “Surtout, pas trop de zèle.” But that has never been his style. Back in the 1980s when he was in the U.S. Attorney’s Office in Boston, Mr. Mueller was up to his eyeballs in a case in which prosecutors framed four innocent men. Two died in prison there before, 30 years on, their families and the other two were awarded $102 million for wrongful prosecution. Mueller never apologised, never even acknowledged the wrongdoing.

Then there was the despicable case of Mueller’s Anthrax investigation after 9/11. There was panic in Washington after 5 people died and 17 were injured when anthrax was sent through the post. A culprit just had to be found. Mueller fingered Steven Hatfill, a government virologist for the crime, destroyed his career, and said nothing when Hatfill was cleared and awarded $5.8 million. Mueller then went after Bruce Edwards Ivins, also probably innocent, but we’ll never know for sure because Mueller drove him to suicide.

Robert Mueller is out of control. On paper, he was supposed to be investigating “any links and/or coordination between the Russian government and individuals associated with the campaign of President Donald Trump.” But there never was any collusion and/or links between the Trump campaign and the Russians. So his mandate also allowed him to investigate “any matters that arose or may arise directly from the investigation” (my emphasis) and “any other matters (my emphasis) within the scope of” the applicable statute.

In other words, the purpose of Mueller’s investigation is to unseat the duly elected President of the United States. But he is dangerous not just to the President. He is also dangerous to rule of law, which is either impartial, pertaining equally to everyone, or else it is a species of arbitrary rule, that is, tyranny. A headline in Politico warns “The special counsel seems to be leaving the president’s children for last.” Politico reports that with relish. But these are police-state tactics. Go after a person’s family. Verdict first, then find the crime.

The motto of the first Earl of Strafford, another nasty piece of work, was “Thorough.” It was the banner under which he endeavoured to enforce the autocracy of Charles I among the Irish and other recalcitrant segments of the population. Robert Mueller is up to something similar. His master is not a king besotted with delusions of absolute power but an engorging leech-like bureaucracy intoxicated by the conviction of its own unassailable virtue and made ruthless by its expropriation of nearly unaccountable power. It is, as the President says, “a witch hunt.” It should be shut down, now, and those responsible for its creation should be held to account.