“When the president says, ‘Make sure to hit the heads of people on the door of the police car,’ or pardons a sheriff accused of racial profiling, it redefines the law as just brute force,” Mr. Waldman said.

Officials in the executive branch and in individual agencies have started to speak out with increasing, and surprising, frequency. A senior Justice Department official wrote a memo after Mr. Trump’s Long Island speech, stating strongly that the agency does not condone brutality. So did several police departments across the country.

Mr. Trump, who spent his early adult years in the crime-ravaged, racially volatile crucible of New York City in the 1970s and 1980s, sees life through the prism of strength versus weakness. On Twitter, as Hurricane Harvey ravaged Texas, Mr. Trump said he had unleashed the force of federal aid. On Sunday morning, as the rains continued, the president tweeted an endorsement of a book by another hard-line law enforcement official accused of civil rights violations: Sheriff David A. Clarke of Milwaukee County, Wis., whom he called “a great guy.”

While Mr. Trump has spoken often of the significance of the rule of law, his actions have raised questions about his commitment to hallmarks of the American system like due process, equal protection under the law, independence of judicial proceedings from political considerations, and respect for orders from the courts.

“I don’t think you have to be a champion of it; all you need to do is comply with it,” said Charles Fried, a Harvard Law School professor who was a solicitor general under President Ronald Reagan.

“And he shows himself absolutely unwilling to respect it,” Mr. Fried said, citing the pardon as a particular thumb in the eye of a judge. “It’s a use of authority specifically to undermine the only weapon that a judge has in this kind of ultimate confrontation.”

The White House declined to address the criticisms on the record, but one official said the president’s actions on immigration enforcement, in particular, had re-established the rule of law instead of ignoring it, lifted the morale of the police, and restored the focus on combating illegal immigration to states instead of the federal government.