Donald J. Trump suggested during a rally in Pennsylvania on Saturday that Hillary Clinton was not “loyal” to her husband, former President Bill Clinton, an insinuation about their relationship that plunged the 2016 presidential race further into a personal battle.

Mr. Trump told the crowd in Lancaster County, about 70 miles west of Philadelphia, that Mrs. Clinton’s only loyalty was to her donors and herself. He added: “I don’t even think she’s loyal to Bill, you want to know the truth. And really, folks, really, why should she be, right?”

A spokesman for Mrs. Clinton did not immediately respond to an email seeking comment.

Mr. Trump, who offered no evidence to support his aspersion, made the remark a day after he told The New York Times in an interview that he was prepared to attack Mrs. Clinton over her husband’s well-publicized infidelities before and during his presidency. In the interview, he called her an “enabler” and said she had attacked the women who said that Mr. Clinton had had affairs with or sexually harassed them.

Mr. Trump, the Republican nominee, has struggled to move past a widely panned performance last week in his first debate against Mrs. Clinton. But he has simply repeated criticisms of her regarding her husband, as well as attacks on a former Miss Universe whom Mrs. Clinton mentioned during the debate as someone Mr. Trump had once belittled.