Michio Kaku, a theoretical physicist and the co-founder of string field theory, from the City College of New York, gives a lecture about the future technology and lifestyle at the IT event "5th Campus Party", at Anhembi park in Sao Paulo, Brazil. YASUYOSHI CHIBA / AFP/Getty Images

The new administration has withdrawn to its corner for now, recovering from a series of court rulings holding that executive orders stopping travel from seven Muslim majority countries are illegal.

But President Donald Trump has vowed to keep trying, even as medical, scientific and technology groups work every possible angle to get employees and students through the new barriers.

Trump frames the travel ban as an issue of national security. In reality, says Dr. Michio Kaku, the nation's safety — along with its prosperity — rely on immigration.

Without immigration, "we'd be a third-rate country," says Kaku, the well-known author of "The Future of the Mind" and other books and a professor of physics at City College of New York. "Most of the prosperity that we see around us is due to the genius of the people that came in the so-called brain drain. There is a brain drain into the United States."

Being able to attract the world's best and the brightest gives the U.S. a huge advantage, Kaku says. It makes for a bigger pie, so everyone gets more.

"The political world view is that it's a zero-sum game," Kaku says. "People think you have to cut the pie thinner and thinner."