Michael Pillsbury, a China expert at the conservative Hudson Institute with close ties to the Trump administration, said that Mr. Trump could blunt the measure’s impact on the trade talks by delaying his signature until after such a deal is reached.

“There’s an ongoing debate in Beijing between reformers who would like phase one and hard-liners who see themselves surrounded by hostile forces led by the United States, including in Hong Kong,” said Michael Pillsbury, a China scholar at the Hudson Institute who advises the Trump administration.