Watergate reporter Carl Bernstein said Sunday that Republicans are coming to a "much greater consensus" that President TrumpDonald John TrumpSchiff pleads to Senate GOP: 'Right matters. And the truth matters.' Anita Hill to Iowa crowd: 'Statute of limitations' for Biden apology is 'up' Sen. Van Hollen releases documents from GAO investigation MORE is unfit to be president following the resignation of Defense Secretary James MattisJames Norman MattisLawmakers push back at Pentagon's possible Africa drawdown Overnight Defense: Book says Trump called military leaders 'dopes and babies' | House reinvites Pompeo for Iran hearing | Dems urge Esper to reject border wall funding request Trump called top military brass 'a bunch of dopes and babies' in 2017: book MORE.

Bernstein, appearing on CNN's "Reliable Sources," said there is concern that Trump is "unfit on psychological grounds" as well as unfit "because of his contempt for the law" and because of his "conduct of foreign policy."

ADVERTISEMENT

“What the Mattis letter has done in a monumental way is to push Republicans into making some real judgments. They’re talking to each other, there is coming to be a much greater consensus that he is unfit to be the President of the United States," Bernstein said. 

Mattis resigned last week from his position as secretary of Defense following Trump's decision to remove U.S. troops from Syria. Mattis wrote in his resignation letter that Trump deserves "a Secretary of Defense whose views are better aligned with yours."

He also expressed concern over Trump's views on traditional U.S. alliances.

"While the US remains the indispensable nation in the free world, we cannot protect our interests or serve that role effectively without maintaining strong alliances and showing respect to those allies," Mattis wrote in the letter.