“That’s just a star,” Mr. Trump said repeatedly.

It was a striking display of self-sabotage from a presumptive presidential nominee and underscored the limitations of Mr. Trump’s scattershot approach during the Republican primaries — not to mention how difficult he often makes it for his campaign team to control him.

Image The tweet that was deleted from Donald J. Trump’s Twitter account.

The rally in Cincinnati had been promoted by Mr. Trump’s team for two days as a chance for him to give a tryout to a potential running mate, former Speaker Newt Gingrich. Periodically, beginning midway through Mr. Trump’s speech, the crowd chanted Mr. Gingrich’s name, but Mr. Trump did not heed its wishes.

Mr. Trump had not discussed the Twitter message at length until Wednesday night, at his rally in Cincinnati, and his remarks seemed to clash with those of his son-in-law, Jared Kushner, an Orthodox Jew, who earlier in the day had defended Mr. Trump in an unusual and candid op-ed article, suggesting that the Twitter post was “careless.”

The attention paid to the controversy had begun to die down by the time Mr. Trump took the stage, and he began to read from notes about the criticism leveled against Mrs. Clinton on Tuesday by the F.B.I. director, James B. Comey.

But within 20 minutes, Mr. Trump tossed his notes aside and moved on to topics closer to home — the criticism he had received for his praise of Saddam Hussein at a rally Tuesday night in Raleigh, N.C.