You wake up, check Twitter, and see that our impetuous president is spewing bile again. But this time, you're the guy he's sliming.

What in the world does that feel like?

"Meh," says David Cay Johnston. "It was just Donald being Donald."

Johnston should also thank Trump. Because you're a nobody until Donald Trump calls you a nobody.

And then, man, you're really someone.

Johnston, 68, is the former Inquirer journalist who on Tuesday got his hands on a copy of Donald Trump's 2005 federal tax return; the document was anonymously mailed to his home in Rochester, N.Y. Its authenticity was verified by the White House and Johnston discussed its findings Tuesday evening on MSNBC with Rachel Maddow.

That didn't stop Trump from tweeting at 6:55 a.m. on Wednesday: "Does anybody really believe that a reporter, who nobody ever heard of, 'went to his mailbox' and found my tax returns? @NBCNews FAKE NEWS!"

To which Johnston tweeted back, "Gee, Donald, your White House confirmed my story. POTUS fake Tweet! Sad!"

Johnston has been all over the media ever since, jawing with Chris Matthews, Lawrence O'Donnell, and Don Lemon; juggling appearances on New Day, Good Morning America, and Democracy Now!; weighing in on the BBC and Canada's CBC and CTV; and doing more print and radio interviews than he was able to recount when we spoke last week.

Boom -- instant somebody!

"At JFK airport yesterday, at least 20 people recognized me and stopped to talk --  a cleaning lady even hugged me," laughs Johnston, a jovial, bearded man who manages to be friendly, accessible, and a know-it-all, all at once. "Some people glared, but that's OK – that's part of the job, too. This is the only business where you get paid to tell the truth as best you can. It's wonderful."

The recent attention has included crude, anonymous calls to Johnston's home and to an apartment he owns in New York City, where his daughter lives. He handled the threats strategically.

"Trump fans call & harass my wife and 1 of my children after I break story White House confirmed. Sad!" he tweeted. "Let's have open debate, not threats."

"We didn't feel threatened, but during Trump's campaign he urged people to commit acts of violence against those who don't agree with him," says Johnston. "That's a sign that someone is a dictator in the making, and I wanted to make a record of it."

For the record, Johnston was a bit of a somebody before he was dismissed as a nobody by the leader of the free world.

He covered the casino industry for the Inquirer from 1988 to 1995 (he lived in Ocean City, N.J., then Cheltenham) before moving to the New York Times. There, he won a 2001 Pulitzer Prize for investigative journalism about tax loopholes and inequities in the U.S. tax code. He has written best-selling books about how America's tax system is rigged to make fat cats fatter.  And last August, he published "The Making of Donald Trump," which presents the 45th president as a preternatural BS artist who has cozied up to the mob, is inept as a businessman, and lies as often about his worth as he does about the sexy women who allegedly crush on him.

As an expert in all things taxes and all things Donald Trump, then, Johnston is exactly the kind of threat the president fears enough to diss in a tweet.

But don't accuse Johnston of personal animus against the man, the way some Trump supporters have this past week.

"Most Americans are motivated by personal views; they truly don't understand that journalism is the only business where you get paid to tell the truth as best you can," Johnston says. "Every word I write is true. I think Donald Trump is manifestly unqualified to be president, but I also find him endlessly fascinating. I started keeping files on him because I knew, the minute I met him, that he was part of an important cultural force in America and, back in 1988, the most important person in Atlantic City."

Johnston is at work on a new book that will cover Trump from his nomination through the end of April; it will be published at the end of 2017. He was researching it in Palm Beach on Tuesday when his daughter, who is his assistant (he has eight grown children and five grandchildren), texted him that a copy of Trump's 2005 taxes had arrived.

She scanned the document and emailed it to her dad. And within 24 hours he was Donald Trump's latest nobody.

Which is really something.