Donald Trump sits in his office with Business Insider founder Henry Blodget. Sam Rega/Business Insider Republican presidential candidate Donald Trump told Business Insider on Thursday that he is demanding a formal apology from The Wall Street Journal for an editorial that panned his free-trade policies.

"In other words, they said, 'Donald Trump made a mistake in his speech.' And I didn't. It was said perfectly," the real-estate mogul said during an interview at his Trump Tower office.

"And when you read my transcript — that's the transcript of my speech," he said, handing out a typed copy of his debate remarks, "it's perfect. So now we've demanded an apology from The Wall Street Journal."

The editorial in question pointed to Trump's strong opposition to the Trans-Pacific Partnership during this week's Fox Business Network debate, which was cosponsored by The Journal.

"Mr. Trump called it a 'terrible deal,' though it wasn't obvious that he has any idea what's in it," the editorial board opined.

The board continued:

His one specific criticism was its failure to deal with Chinese currency manipulation. But it took Rand Paul to point out that China isn't part of the deal and would be happy if the agreement collapsed so the US would have less economic influence in Asia.

This was a reference to a debate exchange in which Trump repeatedly blasted the Pacific Rim trade deal for not addressing Chinese currency manipulation. US Sen. Rand Paul (R-Kentucky), a presidential-candidate rival, memorably shot back that China is not part of the agreement.

But Trump insists that he knew what he was talking about. He pointed to his frequently stated argument that China would enter the trade pact through some kind of "back door," something he said during the debate before he blasted the country's currency-manipulation policies.

"I hope you can cover The Wall Street Journal," Trump told Business Insider. "The Wall Street Journal should call me and ask me if they had any questions. Because I've made 20 speeches on the TPP. They said I didn't know anything about the TPP."

Paul Gigot, editor of The Journal's editorial page, told Business Insider that his newspaper backs the piece.

"We stand by the editorial, which is accurate, though Mr. Trump is welcome to write a letter to the editor in response," Gigot said in a statement, pointing to this week's Trump op-ed in The Journal. "On Tuesday we published his op-ed on China's currency policies."

Donald Trump attacks The Wall Street Journal at a campaign rally. REUTERS/Daron Dean

But Trump's complaints about The Journal were hardly limited to his interview with Business Insider.

In a tweetstorm and in two separate Fox News interviews earlier in the day, the leading Republican presidential candidate called for a resignation, demanded an apology, called staffers there "dummies," and more.

"There's so much misinformation," Trump said on "Fox and Friends." "They aren't a respected paper too much anymore."

"I know that China's not in the deal. And if they look at my speeches, they'll see I talk about it all the time. This deal is going to be a great deal for China," he added on the Fox Business Network.

"I'm suggesting that The Wall Street Journal editorial board doesn't know what they're talking about, that they're third-rate," Trump continued. "They write so many bad editorials. Whoever the editorial-board top person is — and I think I actually know who the top person is — they ought to resign because they're incompetent."

Trump has repeatedly complained about The Journal in the past, including a tweet last month.

"Wall Street Journal loves to write badly about me. They better be careful or I will unleash big time on them. Look forward to it!" he wrote.

On the other hand, as recently as Wednesday, Trump praised the paper's editor-in-chief for his "elegant" moderating during this week's Fox Business Network debate.

And here's Trump series of Thursday tweets stinging the newspaper: