President Trump and Attorney General Jeff Sessions take part in the FBI National Academy graduation ceremony in Quantico, Va., on Dec. 15. (Evan Vucci/Associated Press)

ALL OFFICIALS entering government must swear an oath of loyalty to the Constitution of the United States. President Trump made his own such promise. Yet he appears to believe that the public servants of the Justice Department owe their allegiance not to the Constitution but to him.

The litany of Mr. Trump’s attacks on the integrity of federal law enforcement is lengthy. He reportedly requested personal loyalty from FBI Director James B. Comey and then fired him. He has raged over the refusal of Justice Department leadership to do his bidding. He has demanded an FBI investigation of Hillary Clinton and her former aide Huma Abedin.

New reporting by the New York Times makes clear the depth of Mr. Trump’s disregard for the importance of a nonpartisan and independent Justice Department. Angry over Attorney General Jeff Sessions’s recusal from the Russia investigation, the president reportedly compared Mr. Sessions disfavorably to the unscrupulous New York fixer Roy Cohn. Mr. Trump seems to view Mr. Sessions not as a public servant but as a personal assistant — someone to shield him from political winds, regardless of ethical or legal obligations to the contrary.

The same is true of Mr. Trump’s view of White House counsel Donald McGahn, whom the Times reports Mr. Trump tasked unsuccessfully with talking Mr. Sessions out of his recusal. The White House counsel represents the office of the presidency, not the president’s personal interests. But this distinction appears lost on Mr. Trump.

Not all of the president’s abuses are as explosive as his reprimands of Mr. Sessions or as high-profile as his tweets. But also disturbing is his departure from years of precedent by chief executives who agreed to keep federal prosecutors free of political interference. Instead, Mr. Trump has interviewed three candidates for U.S. attorney, or lead federal prosecutor, in key jurisdictions. One, Jessie K. Liu, is now the U.S. attorney for the District of Columbia. Another, Geoffrey S. Berman, currently heads the office of the U.S. attorney for the Southern District of New York on a temporary basis. Mr. Berman could potentially lead investigations into Mr. Trump’s Manhattan businesses — making Mr. Trump’s personal interaction with him particularly troubling.

Mr. Trump has the constitutional authority to meet with U.S. attorneys and make demands of Mr. Sessions and Mr. McGahn. But what’s legal is different from what’s right. It’s appropriate for the president to confer with the attorney general in setting policy priorities. It’s not appropriate to demand that the attorney general violate departmental ethics rules, interfere with particular investigations or target specific individuals.

Most disturbingly, Mr. Trump seems not to recognize anything wrong or unusual in his conduct. He argues instead that then-Attorney General Eric H. Holder Jr. “protected” President Barack Obama in the same manner Mr. Trump reportedly demanded of Mr. Sessions.

For this reason, it’s the responsibility of those who work with Mr. Trump to restrain him as best they can from destroying the norms he fails to recognize — as Mr. McGahn allegedly failed to do. And it’s the responsibility of Congress to fulfill its constitutional role as a check to the president’s abuses. The Senate can start by refusing to consider any future U.S. attorney nominee who has been interviewed by Mr. Trump.