The Trump administration’s point man on U.S.-China trade negotiations said the U.S. would hold fast to its 90-day deadline for the conclusion of a lasting agreement, adding that the U.S. would impose punishing tariffs on Chinese imports if none is reached.

“If there’s a deal to be done, we’ll make it. The president wants us to make a deal,” said U.S. Trade Representative Robert Lighthizer on CBS on Sunday. “It has to be verifiable, it has to be monitored, it can’t be just vague promises like we’ve seen over the last 25 years.…As...