Attorney General Jeff Sessions was interviewed last week by investigators for special counsel Robert S. Mueller III’s probe into possible election campaign coordination between Russia and Trump associates, the Justice Department confirmed Jan. 23. (Reuters)

THE NATION just got another reminder that the political independence of the nation’s law enforcement system is in jeopardy. It is being protected by a thin line of principled public servants who refuse to bend to the Trump administration and congressional Republicans’ campaign to attack and cajole the FBI into serving political, rather than public, interests.

Axios’s Jonathan Swan reported Monday that Attorney General Jeff Sessions pressured FBI Director Christopher A. Wray to fire Andrew McCabe, a senior FBI official whom President Trump dislikes and has repeatedly excoriated on Twitter. The Post’s Devlin Barrett and Philip Rucker later confirmed much of the story. Mr. McCabe’s sins mostly amount to association with former FBI director James B. Comey, who was himself fired by Mr. Trump for refusing to swear fealty to the president and for declining to treat Mr. Trump’s associates with undeserved leniency.

Even if there were stronger grounds for concern about Mr. McCabe, the attorney general’s overriding interest should have been to protect the integrity of the FBI and do everything possible to guard against it becoming the president’s personal police force, as Mr. Trump appears to want. When the president says he wishes that the attorney general would protect him and when he personally attacks the credibility of seasoned law enforcement agents such as Mr. McCabe, all while the president’s associates are under federal investigation, the only principled response is to insulate the FBI from political pressure by refusing to act on the president’s pique. Mr. Sessions failed this test.

Fortunately, Mr. Wray did not fail it. The FBI director, a veteran of the George W. Bush Justice Department, not only declined to fire Mr. McCabe, but he also reportedly registered his displeasure at being pressured. Mr. Sessions apparently relayed Mr. Wray’s dissatisfaction to White House Counsel Donald McGahn, who felt it best to back off. Mr. McGahn should not have been involved at all. Mr. Sessions should have recognized his ethical lapse after Mr. Wray resisted and not brought it up again. But that would not have served Mr. Sessions’s goal of re-ingratiating himself with Mr. Trump, nor would it have sated ultra-partisan Republicans in Congress who have launched their own offensive on the FBI’s autonomy.

Mr. Trump does not respect the sort of integrity Mr. Wray displayed, he does not understand the proper role of the Justice Department, and he will not stop trying to bend federal law enforcement to his desires. As if to confirm this, he launched another Twitter missive at the FBI on Tuesday, in the process singling out two FBI agents caught up in the president’s ire about the Russia investigation.

The president’s underlying argument — that the Russia probe is an anti-Trump witch hunt led by politically motivated hacks — is a self-serving conspiracy theory that too many in the government have indulged. It is heartening that there are still senior public officials who refuse to compromise key civic principles to accommodate the wayward personality in the Oval Office. It is discouraging that the attorney general is not one of them.