With the welcome mat withdrawn for promising researchers from around the world, America is at risk of losing its longstanding pre-eminence in the sciences.For decades, Bangalore, India, has been an incubator for scientific talent, sending newly minted Ph.D.s around the world to do groundbreaking research. In an ordinary year, many aim their sights at labs in the United States. “These are our students, and we want them to go and do something amazing,” said a professor at the National Center for Biological Sciences in Bangalore, Raj Ladher. But this is not an ordinary year. When Professor Ladher queried some 30...