“It is such as dramatic change from how he portrayed himself when he was in the political field in San Diego,” said Doug Case, a former president of the San Diego Democratic Club. “It looks like maybe his true colors have come out.”

After his political career sputtered, Mr. Navarro continued teaching and writing books about business and investing. But before long, his attention turned to China and its trade practices, which many left-leaning Democrats, including labor leaders, believed were killing American jobs.

Mr. Navarro’s skepticism first emerged in the 1970s while he was a Peace Corps volunteer building and repairing fish ponds in Thailand. He traveled extensively in Asia and said he observed the negative impact China was having on the economies of its neighbors. He became increasingly critical of how China’s trade practices were impacting the United States after its admission to the World Trade Organization in 2001, particularly as many of his business students complained of losing their jobs as a result of Chinese competition.

Mr. Navarro’s views soon hardened and he began publishing a series of anti-China screeds, including “The Coming China Wars,” which Mr. Trump in 2011 listed as one of his favorite books about China, and “Death By China.”

In that book and the accompanying documentary, Mr. Navarro and Mr. Autry excoriated China for unscrupulous economic practices and manufacturing deadly products, like flammable toddler overalls and fake Viagra. They also faulted multinational companies like Walmart for using China to source cheap goods that were putting American manufacturers out of business.

Mr. Navarro’s views caught the attention of then-candidate Donald J. Trump, who shared similar opinions about China’s impact on American manufacturing and was seeking experts with unconventional views that matched his own. Mr. Navarro joined the campaign as an economic adviser in 2016 and quickly gained the trust of Mr. Trump, who refers to Mr. Navarro as “my tough guy on China.”

“My whole philosophy in life and in this job is the Gretzky perspective — skate to where the puck is going to be, anticipate problems that the president is going to want to solve, and get on them,” Mr. Navarro said in an interview.