Ron Vara is the fictional character that Mr. Navarro created and cited as an expert more than a dozen times in five of his 13 books, where he offered searing critiques of China. Mr. Navarro’s use of the fabricated source emerged in October after an Australian scholar reviewed all of Mr. Navarro’s writing and discovered that one of his sources was imaginary.

Mr. Navarro confirmed the authenticity of the memo. It is not clear how widely it was distributed.

“On a daily basis, I speak to, or correspond with, people that I respect, and don’t necessarily agree with, to receive their thoughts on issues critical to American workers and the American people,” Mr. Navarro said. “This kind of active dialogue makes for the best possible decisions.”

He added: “Such a free exchange of ideas is essential to the success of an administration that is simultaneously putting up the best economic numbers in a half century and achieving success after success on the trade front.” He described a new trade deal with Canada and Mexico that is on track to become law as “just the latest big win.”

The memo does not show Mr. Navarro formally endorsing any views, but it lives up to his reputation for seeking to force deep structural changes to China’s economy through tariffs. It outlines the “keep tariffs argument,” which accuses China of stepping up American farm purchases of pork and soybeans only because of its domestic swine fever outbreak. And he claims that recent changes to Chinese law run counter to promises by the country’s officials to protect American intellectual property.

The memo also asserts that Mr. Trump’s tariffs are protecting the United States economy without having any negative effect on growth or the stock market.