On Monday, for the first time ever, Taha Yasseri was turned down for a U.S. visa to attend the prestigious International Conference on Computational Social Science at Northwestern University.

Why? Because, he said, he’s Iranian.

A senior research fellow in computational social science at the University of Oxford, Yasseri’s work on big data and election predictions has brought him around the world, including to the U.S. just this past March. But American politics finally got in the way. He said that a consulate officer explained to him that President Donald Trump’s so-called travel ban had made his requests to get to the campus in Evanston, Illinois, more complicated than usual.

“I appreciated his honesty,” Yasseri told The Daily Beast. “To be honest, I’ve been lucky in that I’ve always been granted a [single-entry] visa.”

Stories of upended travel, aborted education plans, and stymied research projects are becoming more common in the world of Science, Technology, Engineering and Mathematics (STEM) and academia. And they may soon become even more so.

On Tuesday, just one day after Yasseri’s visa request was denied, the Supreme Court ruled in Trump v. Hawaii that the president’s travel ban—in place even while under legal challenge—was, indeed, constitutional. The decision meant the policy will remain in place. And it left academics and scientists fearful that the United States may witness a drain of intellectual talent in the coming years.

Handed down by a 5-4 majority, the ruling prohibits citizens from seven countries—Chad, Iran, Iraq, Libya, North Korea, Syria, Venezuela, and Yemen—from entering the country due to the “national security threat” they supposedly pose.

Critics had argued that the policy was fundamentally racist as it was built on the foundation of Trump’s campaign pledge to stop all Muslims from entering the United States. But over the course of his presidency, Trump narrowed down the policy, including by adding two non-Muslim majority countries to the list.

That proved enough to negate the constitutional concern. But those in the STEM fields say that the practical impact of the ban will be the same as the original incarnation.

“We’re deterring people from coming here,” said Vivek Wadhwa, a distinguished fellow at Harvard Law School and Carnegie Mellon University College of Engineering. “America is now considered hostile to foreigners. Before they can even want to come, they’re turned away.”

The ripple effects of that hostility could be profound, Wadhwa predicted. In the 2012 paper he co-authored, titled “America's New Immigrant Entrepreneurs: Then and Now,” Wadhwa noted that more than a quarter of American engineering and technology startups were founded by immigrants and that in Silicon Valley, nearly half of startups are immigrant-founded. When it came to patents, more than 60 percent of filings were done by immigrants; over 40 percent of international patent applications on behalf of the American government included an author who wasn’t an American citizen.

The travel ban could fundamentally change the American economy by drying up that source of innovation.

“With this brain drain happening, we’re arming our competitors in China and South America with the greatest threat to American security,” said Wadhwa. In particular, there’s the fact that “we’ve been training the smartest students from China and sending them back home,” he said. “China is catching up to America in artificial intelligence and gene editing and robotics. We never thought China would be able to compete with the U.S. but China is on par with the U.S. right now.”

Even before the Supreme Court’s decision on Tuesday, the effects of the ban were become evident in a variety of fields. Dr. Atul Grover, the executive vice president of Association of American Medical Colleges, said that over the preceding year, there had been about a 22 percent drop in the number of people requesting a student visa from the seven countries on the president’s list.

“For a one year difference that is pretty significant,” Grover said.

But, he added, the actual impact is likely to be even more severe. He expected prospective medical students from countries not on the current list to balk at applying to schools in the United States out of fear that their nations may be added by Trump at a later date. In addition, students with spouses from countries currently under the ban would have to weigh the possibility of splitting up their family if they choose to study in the United States.

“We are already looking at a physician shortage,” Grover said. “While we have increased the number of graduates from U.S. medical schools, we are still reliant on international graduates to serve people, particularly in underserved areas. That will be harder and harder to fill these positions if we have fewer applicants. Or it may be that these applicants are as qualified as they are in the past. We’ve had our choice of the best and the brightest in the past. But now, people might look elsewhere.”

Under the travel ban, individuals from the seven targeted countries can still apply for, and be granted, student and exchange visas. But the incentives for requesting each are greatly diminished. Progress in STEM fields take an immense amount of work and time, from producing the research, to building a company, to seeking investment of capital. If a ban or the threat of deportation holds, that incentive to stay in the country is diminished.

This will impact both those here and those seeking to come. According to data provided by the Institute of International Education, there were 25,751 students from the seven banned countries who studied in the United States during the 2016-17 calendar year. Advocates expect that number to diminish and those students to look abroad for career opportunities.

Meanwhile, the Department of Justice reported that the number of visas issued by the to students from Iran, Libya, Yemen, and Somalia in the first three months of this year was just 298. “This is less than a quarter of the volume needed to be on track for 2016 student visa levels,” the last full year before the ban took effect, Justice Stephen Breyer noted in his dissenting opinion.

Educators, likewise, will face diminished incentives to work at, or even collaborate with, U.S. institutions. In Yasseri’s case, the inability to attend the conference at Northwestern was a major professional setback, depriving him the opportunity to present groundbreaking research, network with others in the field, and participate in a conference that he helped coordinate and plan.

It’s one of the reasons why Yasseri—who is set to become a British citizen by the end of the year—said he has never entertained the United States as a potential research destination. He left for Europe 12 years ago from Iran, and while many of his friends went to the America, he found the single entry visas students had to deal with cumbersome. “If they left the country, they had to reapply for a visa,” he pointed out. “I didn’t want to be trapped in a single country.”

So Yasseri went around that. He earned his Ph.D. in Germany and is conducting research in the United Kingdom. With a British passport, he thinks traveling to the United States might become easier, and he might even look into doing a sabbatical in the U.S.

But settling in America permanently remains out of the question.

“Even if I got a visa, my family would not be able to visit,” Yasseri said.