STATE DEPARTMENT Inspector General Steve Linick was asked by House Democrats last year to investigate whether Secretary of State Mike Pompeo abused his authority in declaring an emergency to ram through arms sales to Saudi Arabia in spite of congressional opposition. Mr. Linick was also reportedly probing Mr. Pompeo’s use of an aide to perform personal errands for himself and his wife. Mr. Pompeo asked President Trump to fire Mr. Linick — and late on Friday, the president did just that, in a blatant attempt to shield the secretary of state from accountability.

The blunt dismissal of a nonpartisan official whose job it is to provide an independent evaluation of just the sort of allegations Mr. Pompeo was facing would be shocking — if it were not just the latest step in a campaign by Mr. Trump to eliminate accountability across the federal government. Mr. Linick is one of four inspectors general fired or replaced by Mr. Trump since April 3, when he ousted the intelligence community IG who forwarded a whistleblower’s account of his wrongdoing on Ukraine to Congress.

The purge makes a mockery of Congress’s attempt to protect the independence of inspectors general, including a legal requirement that they not be removed without written justfication. In the case of Mr. Linick, Mr. Trump dispatched a vague letter to House Speaker Nancy Pelosi (D-Calif.) saying he “no longer” had “the fullest confidence” in the IG. But Mr. Pompeo did not hesitate to blurt out the real reason Monday: Mr. Linick was not doing his bidding. He “wasn’t performing a function in a way that we had tried to get him to,” Mr. Pompeo said in an interview. But it is not the inspector general’s job to do what the secretary of state demands — especially when it comes to investigating his own behavior.

Mr. Linick, who had held his post since 2013, had a record of holding secretaries of state of both parties to account. In 2016, he issued a critical report on Hillary Clinton’s use of a private email server, fueling a controversy that helped get Mr. Trump elected. But he also reported last year on the harassment of career staff in the State Department accused of disloyalty to Trump, and he cooperated with the House’s impeachment inquiry.

Several reports said Monday that Mr. Linick was nearly finished with his inquiry into Mr. Pompeo’s circumvention of Congress on Saudi Arabia. His probe of the secretary’s misuse of staff for personal errands, such as retrieving his dog from the groomer, would likely reinforce what has been a pattern of questionable behavior by Mr. Pompeo, who also used State Department aircraft for multiple visits to his native Kansas at a time when he was considering a run for senator.

Congressional Democrats have promised an investigation of Mr. Linick’s firing; Ms. Pelosi suggested it could have been an illegal act of retaliation. Republican senators, including Susan Collins (Maine) and Charles E. Grassley (Iowa), suggested the firing was not in keeping with the requirement of written justification. The question, as always, for these and other Republicans is whether they will insist that Mr. Trump observe the rule of law — or simply roll over once again.

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