President Donald Trump may be unwilling to release his income tax returns because he fears the world will know he is nowhere near as wealthy as he has claimed, according to Pulitzer Prize-winning journalist David Cay Johnston.

“He’s afraid that everyone is going to discover that his claims of being a billionaire are nonsense,” Johnston, the author of “The Making of Donald Trump,” said in an interview on the Law&Crime Network program Brian Ross Investigates. “He’s a wealthy man, but he’s in the tens of millions or hundreds of millions class – not, as he’s claimed, a $10-plus billionaire.”

Since he first launched his candidacy for president, Trump said he couldn’t hand over his tax returns because he was being audited. He said he would release them as soon as the audit was over, but he still has yet to do so.

While Congress and Manhattan District Attorney Cyrus Vance are currently pursuing the records, Trump is waging a fierce legal battle against releasing them. In the New York case, Vance is investigating whether the Trump Organization broke the law when it paid hush money to two women to keep them silent about their respective relationships with him.

Now that a federal appeals court has ruled against President Trump, his attorneys are expected to appeal to the Supreme Court in order to block the Manhattan grand jury subpoena for the returns.

In the 1990s, Johnston said, Trump had two income tax fraud trials over his 1984 tax returns. In one case, his then-accountant Jack Mitnick testified that the signature on the returns was his, but that his firm had not prepared the returns.

Johnston first reported in his book that Trump had falsified the documents by using a photocopy machine.

“One of the reasons Donald Trump doesn’t want Cy Vance to get his hands on the more recent tax returns prepared by the Mazars accounting firm – I think there’s a very good chance that what he submitted to the government doesn’t line up with what was prepared by his accountants,” Johnston said.

Johnston said he does not believe the Supreme Court will take Trump’s case to block the Manhattan subpoena – it’s been the law since Thomas Jefferson that a president can’t fight a subpoena in this way, he said.

“The subpoena, by the way, has nothing to do with his presidency,” Johnston said. “It is for business records and tax returns before he took office. If the Supreme Court does take the case, I think it will be solely for the purpose of writing an opinion that slaps down Trump’s assertions that he is exempt, even as his lawyer said in this case, from a criminal inquiry were he to shoot someone on Fifth Avenue.”

Watch the full interview below, starting around the 12:30 mark:

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