2020 White House candidate Sen. Michael Bennet, D-Colo., said Monday that some of his GOP colleagues in the Senate privately tell him how "horrified" they are by President Trump's behavior.

Appearing on CNN, Bennet was asked if he heard more "private" support for Trump from Republican lawmakers than what was known publicly. Bennet insisted it was quite the opposite.

"They’re horrified that he invited Ukraine to interfere in our elections, they are horrified that the chief of staff admitted it was a quid pro quo. They're particularly horrified by what president did in northern Syria by abandoning the Kurds there, something I think there's a consensus in the Senate -- no other president in history would have done," Bennet elaborated. "We have to stand up to tyrants here and abroad... That's why we have to make America America again."

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He added, "We’ve had enough of this guy and I do think their president -- Republicans in the Senate, who are getting awfully tired of having to defend him."

Trump frequently has denied doing anything improper in his July phone call with his Ukrainian counterpart. Acting Chief of Staff Mick Mulvaney on Sunday denied his comments last week about withholding aid money to Ukraine constituted a quid pro quo. On Turkey's Syria incursion, the president said over the weekend: "We are not a policing agent... It is time for us to go home."

Bennet has long been struggling to gain traction on the campaign trail, polling at just one percent in the latest Fox News Poll. The Colorado lawmaker failed to meet the requirements to participate in the Democrats' last two debates and likely will not qualify for the next debate in November.

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During the interview, he also went after Sen. Elizabeth Warren, D-Mass., who he said was "not being honest" about how she would fund "Medicare-for-all." Warren has pledged to reveal how the U.S. would pay for it soon, amid concerns from critics that it could involve a tax hike for the middle class.

"I think that her plan, which costs $33 trillion, is the equivalent of 70 percent of all the taxes that the federal government will collect over the next ten years," Bennet continued. "It hasn't been explained to the American people. It's a sound bite, and more than that, it's not based on common sense."