President Donald Trump’s escalation of trade threats against China reflects his belief that Washington increasingly has the upper hand in the dispute, administration officials said, adding he is prepared to withstand pressure from U.S. businesses that might suffer from the conflict.

Mr. Trump caught Chinese officials off guard with his announcement Monday evening about potential new tariffs. Should China retaliate against U.S. trade policies, the White House said, the U.S. would apply tariffs of 10% on as much as $400 billion...