WASHINGTON—Howard Lutnick’s journey from Wall Street veteran to one of President Trump’s most hawkish trade advisers began with a speech at an October campaign rally at Madison Square Garden. Lutnick extolled the virtues of tariffs and argued that the duties could at least in part replace the U.

The billionaire Wall Street CEO fielded questions about tariffs, China's AI progress, broadband access, allegiance to Trump and the revival of American mining and semiconductor production.