Donald TrumpDonald John TrumpBusiness, ballots and battling opioids: Why the Universal Postal Union benefits the US Sanders supporters cry foul over Working Families endorsement of Warren California poll: Biden, Sanders lead Democratic field; Harris takes fifth MORE targeted Republican presidential rival Ben CarsonBenjamin (Ben) Solomon CarsonTrump heads to heart of resistance in California Trump awards Yankees legend Mariano Rivera the Medal of Freedom HUD watchdog finds no misconduct by Carson in furniture controversy: report MORE on Tuesday morning, suggesting the retired neurosurgeon doesn’t have the temperament for the Oval Office.

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"It's not his thing. He hasn't got the temperament for it," Trump said during an interview on ABC's "Good Morning America."

"I think that Ben just doesn't have the experience," Trump added on the program while promoting his new book.

Carson has surged ahead of Trump in recent polls, becoming the first Republican to edge out the celebrity real estate tycoon in more than three months.

Carson led Trump by 6 points, 29 to 23 percent, in a Wall Street Journal/NBC News poll released Monday. A New York Times/CBS poll released last week also found Carson ahead of Trump.

"Carson wants to cut Medicare," Trump said during another interview on "Fox & Friends."

"To me, that's the end of his campaign," Trump said, launching another attack line.

He also focused on Democratic front-runner Hillary Clinton during his "Good Morning America" appearance, suggesting she was "bluffing" about wanting to face him in the general election.

“She’s done a terrible job as secretary of State. The world blew up around her," Trump said. "In my opinion, she's the nominee unless she gets indicted."