Author Michael Wolff said people in the White House believe that if special counsel Robert MuellerRobert (Bob) MuellerSenate Democrats urge Garland not to fight court order to release Trump obstruction memo Why a special counsel is guaranteed if Biden chooses Yates, Cuomo or Jones as AG Barr taps attorney investigating Russia probe origins as special counsel MORE looks into President TrumpDonald TrumpJulian Castro knocks Biden administration over refugee policy Overnight Energy & Environment — League of Conservation Voters — Climate summit chief says US needs to 'show progress' on environment Five takeaways from Arizona's audit results 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."
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.
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 ManafortPaul John ManafortDOJ investigating one-time Trump campaign adviser over alleged ties to Qatar: report Foreign lobbyists donated over M during 2020 election: report Former Mueller prosecutor representing Donoghue in congressional probes: report MORE was indicted on charges including conspiracy against the United States, tax fraud and money laundering in connection with the Russia probe.