That fear comes as China has started to experience a reverse brain drain. Over the last decade, a growing number of Chinese scientists have been lured back to the country by the promise of ample funding, impressive titles and national pride. More recently, scientists returning to China have cited a hostile environment in the United States as a factor.

Westlake University, a research university in the eastern Chinese city of Hangzhou, has recruited an impressive roster of talent, including many who once held faculty positions at top American schools. In August, Westlake announced several new hires, including a tenured professor from Northwestern University and another from the University of Illinois at Urbana-Champaign.

Shi Yigong, a prominent molecular biologist and the president of Westlake University, said colleagues had complained about the atmosphere of suspicion in the United States. “For those who have chosen to relinquish their jobs in the U.S., sometimes I do hear stories of a bitter nature,” Dr. Shi said. “I think some of them, not all of them, have been singled out for what I think was pretty harsh treatment.”

At least one person, though, is determined to stay in the United States: Dr. Hu.

The son of a factory worker, he grew up in a poor village in the eastern Chinese province of Shandong and said his interest in science began at a young age. In elementary school, he rigged a simple radio by wiring a speaker with scrap mineral and connecting it to a makeshift antenna he hung from a tree.

After earning advanced degrees in China, he left the country in 1997 with his wife and worked in several countries before obtaining a second Ph.D. in physics in Canada. Like countless immigrants before him, he moved to the United States in 2013 with hopes for a better life and career.

He has sacrificed too much to give it all up now, he said.

He would rather stay in the United States to contribute not just to science, his first love, but also to his new passion: promoting justice. “I have no interest in politics and know almost nothing about it,” he said. “But I know that targeting Chinese and Asian Americans — that will not make the United States strong.”

Javier C. Hernández and Amy Chang Chien contributed reporting.