WASHINGTON—For Peter Navarro, President Donald Trump’s trade guru, it’s been quite a turnaround.

Last spring, he was running the White House’s Office of Trade and Manufacturing Policy, an impressive-sounding group that consisted of himself and an aide in a single room in a building across the alley from the Oval Office. He couldn’t persuade the White House to hire him an administrative assistant, and he reported to the president through his rival, National Economic Council Director Gary Cohn.

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