REDDING, Calif. — In a speech in which he promoted the backing of Chinese-Americans in Los Angeles and called protesters at a rally in San Jose “thugs,” Donald J. Trump on Friday sought to project support from African-Americans for his campaign on a single man in the audience.

Mr. Trump, at a rally here, began speaking about a previous rally in Arizona in which a black supporter was arrested after punching a protester.

“We had a case where we had an African-American guy who is a fan of mine,” Mr. Trump said of an event in Arizona in March. “In fact I want to find out what’s going on with him.”

As his voice trailed off, Mr. Trump noticed a man in the crowd.

“Oh look at my African-American over here,” Mr. Trump said. “Are you the greatest? Do you know what I’m talking about?”