Author Michael Wolff said people in the White House believe that if special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE looks into President Trump Donald John TrumpObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE's finances in the Russia probe, the president is "sunk."

"People don't think in the White House — don't think that he colluded with Russia," Wolff, the author of a controversial new book on the Trump White House, said during an interview with CNBC's "Squawk Box."

"They do think that if the investigation goes near his finances, he's sunk."

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Wolff also said he was "confident" in the accuracy of everything printed in his book, "Fire and Fury: Inside the Trump White House."

The book, released last week, has sparked controversy. Trump and his allies have criticized the book and sought to defend the president against the allegations made in it.

Mueller is currently investigating Russia's interference in the 2016 presidential election and potential collusion between the Trump campaign and Moscow.

According to a report published Monday, Trump's legal team is talking about possible formats in the case that Mueller asks to interview Trump in the Russia investigation.

Trump has repeatedly dismissed the Russia probe as a "witch hunt" and denied collusion.

In July Trump warned Mueller against investigating his family's finances beyond the probe into ties between his campaign and Russia.

Last year, former Trump campaign chairman Paul Manafort Paul John ManafortOur Constitution is under attack by Attorney General William Barr Bannon trial date set in alleged border wall scam Conspicuous by their absence from the Republican Convention MORE was indicted on charges including conspiracy against the United States, tax fraud and money laundering in connection with the Russia probe.