Sen. Ted Cruz on Friday accused GOP presidential front-runner Donald Trump of telling Americans he’s lying to them, blasting comments from Mr. Trump’s convention manager that the brash billionaire is projecting a public image he’s going to be able to dial down.

Speaking to reporters in Pennsylvania, Mr. Cruz said Mr. Trump’s “lobbyists” “have taken over his campaign.”

“And they’ve gone down and told Republican party bosses that everything Donald has said on the campaign is just a show; he doesn’t believe any of it,” Mr. Cruz said. “He’s not going to build a wall. He’s not going to deport anyone. This is just a lie.”

“And I will say to the millions of Americans who are frustrated with politicians who are lying to them: Donald is telling us he’s lying to us,” he said.

Paul Manafort, Mr. Trump’s convention manager, told party officials at the Republican National Committee’s spring meeting in Florida on Thursday that Mr. Trump is going to be able to dial back his brash public persona going forward.

“When he’s out on the stage, when he’s talking about the kinds of things he’s talking about on the stump, he’s projecting an image that’s for that purpose,” Mr. Manafort said, according to The Associated Press.

“He gets it,” Mr. Manafort said. “The part that he’s been playing is evolving into the part that now you’ve been expecting, but he wasn’t ready for, because he had first to complete the first phase. The negatives will come down. The image is going to change.”

Mr. Cruz said Friday that no one will celebrate more if Mr. Trump wins the GOP nomination than the campaign of Democratic presidential front-runner Hillary Clinton.

“Donald Trump may be the only human being on earth who Hillary can beat,” he said.

Mr. Trump said at a rally in Harrisburg, Pennsylvania, on Thursday that he’s not sure he’s quite ready to act more “presidential.”

“My wife is constantly saying, ‘Darling, be more presidential,’ ” Mr. Trump said. “I just don’t know that I want to do it quite yet … because we have a job to do.”

“I’ve got two leftovers. I have to finish that, OK?” he said. “We have to. We have to. And we’re doing so good, and we have to be tough for a little while.”

“At some point, I’m going to be so presidential that you people will be so bored, and I’ll come back as a presidential person and instead of 10,000 people, I’ll have about 150 people,” he said. “And they’ll say, ‘But boy, he really looks presidential.’ “