Donald Trump said Wednesday that his GOP primary rivals who have failed to follow through on their promise to support the party’s eventual nominee should be barred from seeking elected office again.

“They broke their word,” Mr. Trump, the presumptive GOP presidential nominee, said during a rally in Maine. “In my opinion, they should never be allowed to run for public office again because what they did is disgraceful.”

Fueled by fears that Mr. Trump would launch a third-party bid, the Republican National Committee urged the crowded Republican field of presidential candidates to sign a pledge last year that called on them to “endorse the 2016 Republican presidential nominee regardless of who it is” and forgo running as an independent or as a write-in candidate.