WILMINGTON, N.C. — Donald J. Trump on Tuesday appeared to raise the possibility that gun rights supporters could take matters into their own hands if Hillary Clinton is elected president and appoints judges who favor stricter gun control measures.

Repeating his contention that Mrs. Clinton wanted to abolish the right to bear arms, Mr. Trump warned at a rally here that it would be “a horrible day” if Mrs. Clinton were elected and got to appoint a tiebreaking Supreme Court justice.

“If she gets to pick her judges, nothing you can do, folks,” Mr. Trump said, as the crowd began to boo. He quickly added: “Although the Second Amendment people — maybe there is, I don’t know.”

Oblique as it was, Mr. Trump’s remark quickly elicited a wave of condemnation from Democrats, gun control advocates and others, who accused him of suggesting violence against Mrs. Clinton or liberal jurists. Bernice A. King, daughter of the Rev. Dr. Martin Luther King Jr., called Mr. Trump’s words “distasteful, disturbing, dangerous.”

Mrs. Clinton’s running mate, Senator Tim Kaine of Virginia, expressed disbelief. “Nobody who is seeking a leadership position, especially the presidency, the leadership of the country, should do anything to countenance violence, and that’s what he was saying,” Mr. Kaine said in Austin, Tex. He called Mr. Trump’s remark “a window into the soul of a person who is just temperamentally not suited to the task.”

And Dan Gross, the president of the Brady Campaign and Center to Prevent Gun Violence, which has endorsed Mrs. Clinton, said Mr. Trump’s statement was “repulsive — literally using the Second Amendment as cover to encourage people to kill someone with whom they disagree.”