Republican presidential candidate Donald TrumpDonald John TrumpTrump knocks BuzzFeed over Cohen report, points to Russia dossier DNC says it was targeted by Russian hackers after fall midterms BuzzFeed stands by Cohen report: Mueller should 'make clear what he's disputing' MORE on Tuesday accused rival Ted CruzRafael (Ted) Edward CruzGroup aiming to draft Beto O’Rourke unveils first 2020 video Howard Dean looking for a 'younger, newer' Democratic nominee in 2020 Congress can stop the war on science MORE of having “a mental problem.”

“Seriously, he’s got a mental problem,” Trump told host Maria Bartiromo on Fox Business Network’s "Mornings with Maria."

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“There’s never been any politician — or almost anybody in my life — that I’ve seen that lies so much.”

Trump said Cruz is misleading Americans about Trump's fundamental policy positions on hot-button topics including gun control and healthcare.

“He will say I’m against the Second Amendment,” he said. “He will say I’m terribly in favor of ObamaCare, which is ridiculous. These are things that are staples of what I'm about.

"I’m totally in favor of the Second Amendment. ... I want the Second Amendment — I’d strengthen it if anything."

Trump added that other GOP White House hopefuls have slammed Cruz for dishonesty.

“By the way, I’m not the only that said it,” he said. "Marco RubioMarco Antonio RubioOvernight Defense: Second Trump-Kim summit planned for next month | Pelosi accuses Trump of leaking Afghanistan trip plans | Pentagon warns of climate threat to bases | Trump faces pressure to reconsider Syria exit Pressure mounts for Trump to reconsider Syria withdrawal Senate Republicans eye rules change to speed Trump nominees MORE called him a liar during the debate.”

Cruz has repeatedly accused Trump and Rubio of not being sufficiently conservative. He accused both men on Monday of shouting “liar” at critics anytime their actual beliefs are put in the spotlight.

“It is not being honest or candid for either Marco Rubio or Donald Trump to pretend that their records are different than what they are and simply yell and scream at anyone who points to the words that have come out of their own mouths,” Cruz said.