Journalist Carl Bernstein challenged Fox News on Sunday to dispatch reporters to Republican lawmakers to ask questions about President Trump Donald John TrumpHR McMaster says president's policy to withdraw troops from Afghanistan is 'unwise' Cast of 'Parks and Rec' reunite for virtual town hall to address Wisconsin voters Biden says Trump should step down over coronavirus response MORE's fitness to serve amid questions about the president's mental health.

"Let them send twenty reporters to talk to every Republican senator, every Republican congressman and come back and tell us what these people are saying in private, on background," Bernstein told CNN's Brian Stelter on "Reliable Source," referring to questions on Trump's mental fitness.

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"I come back to Fox time and again because this is a chance to show that they can be fair and balanced, that they are capable of being a real reporting organization," he said invoking the outlet's fair and balanced slogan.

Questions surrounding Trump's mental health surfaced this week after author Michael Wolff claimed in his new book "Fire and Fury: Inside the Trump White House," aides are concerned about Trump's mental stability and believe that he is “incapable of functioning in his job.”

White House press secretary Sarah Huckabee Sanders pushed back on the assertion during an interview with "Fox and Friends" on Friday.

“It's absolutely outrageous to make these types of accusations and it's simply untrue, and it’s sad that people are going and making these desperate attempts to attack the president,” she said.

Trump himself blasted the claim, calling himself "a very stable genius" in a tweet on Saturday.