Presidential historian Douglas Brinkley on Friday predicted that public support for President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE will collapse as House Democrats continue their impeachment inquiry against him.

“It just tells you what deep trouble Donald Trump is in. I mean, when you have 50 percent of the country wanting you not just impeached but removed from office, and the game hasn’t even gotten fast yet,” Brinkley said Friday morning on CNN, where he serves as a contributor.

“I think once the vote is taken by Congress to impeach him and he’s wearing the ‘I’ on his chest, you’re going to see that movement grow even more,” Brinkley predicted.

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He added of Trump, “It tells you he doesn’t have a lot of friends. He’s a base politician. He doesn’t know how to turn this around.”

CNN presidential historian Douglas Brinkley on a recent poll showing 50% of Americans support impeaching and removing Trump from office:

After Congress votes, "you're going to see that movement grow even more... He's a base politician. He doesn't know how to turn this around." pic.twitter.com/wR9iCB4Jho — New Day (@NewDay) November 29, 2019

Brinkley noted the successful campaigns of politicians from opposing parties that came after previous presidents faced political fallout.

"I think the Democrats might want to look at the way Jimmy Carter Jimmy CarterTexas Democrats roll out first wave of planned digital ads as Election Day nears Chris Matthews ripped for complimenting Trump's 'true presidential behavior' on Ginsburg Warning signs flash for Lindsey Graham in South Carolina MORE pulled off victory in 1976. He took the high road. He ran on saying, I will never tell a lie to you," Brinkley said. "He didn't have to say Nixon's lies or Lyndon Johnson's lies, just that I am clean, good governance coming your way if you vote for me."

Polling on impeachment has fluctuated in the nine weeks since Democrats launched their probe.

A Quinnipiac University poll released Tuesday found a slight shift in the president's direction on impeachment. That survey found 45 percent in favor of Trump’s impeachment and removal, with 48 percent against it. That was a reversal from the poll's findings the previous month.

However, a CNN poll conducted after the first week of public hearings in the inquiry found that 50 percent of Americans said Trump should be impeached and removed from office, while 43 percent said he should not be — the same margin from a poll conducted in October.