Similar complaints dogged the use of stop-and-frisk in Chicago, prompting the Police Department to make an unusual concession: It now allows an independent third party to monitor its use.

Mr. Trump remains an unabashed fan of the tactic and has glossed over the legal and racial objections to its use for years. In 2013, after Judge Scheindlin’s ruling, Mr. Trump took issue with those who would end the strategy.

“NYC politicians better stop pandering — ending stop & frisk would be a disaster,” he wrote on Twitter.

As a presidential candidate, Mr. Trump has repeatedly praised the procedure as a proven approach for reducing crime, holding up New York City’s experience as an example.

“Stop-and-frisk is a very positive thing,” he said a few weeks ago.

Mr. Trump is drawing historically low support from African-Americans, according to several polls, and he has repeatedly stumbled in his attempts to appeal to them. He earned ridicule a few weeks ago when he told blacks that “you’re living in your poverty, your schools are no good, you have no jobs, 58 percent of your youth is unemployed — what the hell do you have to lose?”

Wednesday was a chance for Mr. Trump to try a different approach, by speaking to black pastors. When asked about recent police shootings of black people in Tulsa, Okla., and Charlotte, N.C., he even seemed to fault the officer in the Tulsa case, saying, “I don’t know what she was thinking, but I’m very, very troubled by that.”

But Mr. Trump’s choice of the 85-year-old Mr. King to introduce him was unusual: Mr. King was convicted of manslaughter in 1966, though he was later pardoned; he has been investigated for possible connections to organized crime; and he has no political experience. He is best known for promoting many of boxing’s highest-rated matches, like the 1974 “Rumble in the Jungle” between Muhammad Ali and George Foreman in Zaire.