“He literally doesn’t know anything,” David Cay Johnston says of Donald Trump. The Pulitzer Prize-winning investigative reporter is at the National Press Club Thursday night, talking up his new biography of the Republican presidential nominee. And here’s a spoiler: he’s not a fan.

Johnston calls Trump “a con man,” says he’s “not a successful businessman,” and relays that his reporting on “everything Donald wants to make sure you don’t know” includes no evidence the real estate mogul is actually a billionaire. But the author of “The Making of Donald Trump” is just getting started.

Johnston rips Trump’s ignorance on business, foreign affairs and the basic principles of American government. He says the mogul “has no regard for his fellow man,” as evidenced by fraud at his Trump University, among other things. He hits him on embracing a host of unsavory characters throughout his life, including swindlers, cocaine traffickers, mob associates and, of course, friends of Russian President Vladimir Putin.

Yet the biographer says the most troubling thing about Trump is his “philosophy of revenge” — a driving desire to get even or, to quote his favorite Bible passage, take “an eye for an eye,” as opposed to turning the other cheek.

Johnston does talk in passing about some of Trump’s better attributes, if they can be called that. The mogul isn’t a homophobe, and “like Bernie Sanders, [he] has tapped into the normal response of the people being hurt” in an economy that’s still not working for many Americans.

Still, the damning phrase the investigative reporter keeps repeating is that “Donald just makes it up” on most subjects.

He says Trump supporters are “voting for a man who doesn’t know anything about anything” except, perhaps, how to acquire cash that provides the appearance of great wealth.

It’s safe to assume Trump isn’t thrilled about all this. Johnston tells the crowd the mogul doesn’t have a nickname for him yet — “It’s probably ‘Fat Boy’ or something” — but recalls how Trump called him at home on April 27, a few months before his book would drop.

First he turned on charm, praising some of Johnston’s previous work. But he soon cut the music, saying in a classic Trump move that he’d sue the reporter if he didn’t like what he wrote.

Johnston’s response, which prompted Trump to end the call: “Do what you need to do, Donald.”

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