The dollar gained and investors sold off stocks after the president-elect promised to levy new restrictions on the United States’ biggest trade partners.

President-elect Donald J. Trump is assembling a team of aides bent on confrontation with China. But he also has advisers who do business there, including Elon Musk.

Foreign leaders have rushed to ingratiate themselves with Donald J. Trump in recent days, nervously recalling the clashes, insults and feuds of his first presidency.

Beijing is expecting more volatility and competition with the United States, though a lackluster economy may limit China’s options for pushing back.