He has long branded China as an economic enemy and accused it of effectively waging an economic war on the United States by subsidizing exports and impeding American imports. To flip the dynamic, Mr. Navarro has advocated the type of aggressive trade policy toward China that Mr. Trump is now pursuing, including stiff tariffs on as much as $150 billion worth of Chinese goods and as investment restrictions.

Mr. Navarro has long accused China of flooding the United States with cheap metals and was one of the only advisers pressing Mr. Trump to proceed with sweeping steel and aluminum tariffs on all countries. Mr. Navarro — and Mr. Trump — say the measure will ultimately pinch China, which they accuse of routing steel and aluminum through other countries to avoid restrictions that are already in place on Chinese metals.

Mr. Navarro also helped orchestrate an investigation into China’s abuse of American intellectual property, which resulted in the United States threatening to impose tariffs on everything from medical devices to flat-screen televisions. “What the United States is doing is strategically defending itself from China’s economic aggression,” Mr. Navarro said when the measures were announced in March.

He doesn’t much like Nafta or other trade agreements, either

Mr. Navarro came to the White House with multiple trade actions written and ready for the president’s signature, including a directive to begin withdrawing from the North American Free Trade Agreement.

That attempt was blocked by other White House officials, but the 1994 agreement with Canada and Mexico is on the verge of collapse amid deep disagreements with the United States, which has made a series of demands that the other nations consider nonstarters. Mr. Trump, who has called Nafta the worst trade deal in history, has continued to threaten to withdraw from the pact, which has put him at odds with business groups and many Republican lawmakers.

Mr. Navarro had an early success — he drafted the presidential memorandum to officially withdraw the United States from the Trans-Pacific Partnership, an Obama-era trade deal, which the president signed on his fourth day in office. That pact, which would have set new terms for trade and business investment among the United States and 11 other Pacific Rim nations, was criticized by Mr. Trump as “ridiculous.”