Biographer David Cay Johnston rips into detractors who didn't heed his warnings about 'dictator Trump'
Donald Trump greets supporters and tourists at the Trump Tower on July 22, 2015 in New York City

An author who literally wrote the book on Donald Trump's shady financial history went off on detractors who failed to heed his warnings even prior to 2016.

Pulitzer winner David Cay Johnston told CNN's Ana Cabrera Saturday that the laws governing the release of presidential tax returns are "incredibly clear" — and noted that Treasury Secretary Steve Mnuchin is "really sticking his neck out" and risking jail time in his refusal to cooperate with congressional investigators seeking to get them.

"Why would he be willing to potentially go to jail, potentially be removed from office by rejecting this request from the house ways and means committee?" Cabrera asked Johnston.

"Because Donald Trump appoints people who either lack moral character or who are willing to pledge personal loyalty to him," the biographer said.

He then launched into a passionate rant about the man he's been covering for years.

"I've been warning people as the person who's covered Trump longer than anybody else, for more than 30 years, from before the time he took office, if Donald got in the White House he would act like a dictator because he does not know what's in the Constitution and he doesn't care," Johnston said.

"He believes in his own mind that he should run the country and he tells us all the time he's smarter than all of us, everyone else who stands in his way is an idiot or a fool or a traitor or something else," he added. "That's the language of dictators, not of someone who under our constitution is there to faithfully execute the laws that Congress has passed."

As for the reason Mnuchin and Trump's continued refusal to provide the public with the president's tax return, Johnston said the answer is simple.

"Donald Trump is not a billionaire," he said. "His biggest concern is that he'll be exposed for the fraud he is, in finance but he's also concerned it will get into money he likely laundered for people who were not just Russians but in the Middle East and elsewhere in real estate transactions."

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