On the last Monday in June I ran into my lab mate, close collaborator and friend, Mehraveh Salehi. We were at the Organization for Human Brain Mapping Conference in Vancouver.

Salehi had just learned that the U.S. Supreme Court would reinstate parts of Pres. Donald Trump’s travel ban within 72 hours. Salehi is Iranian, living 6,000 miles from home to work at Yale University’s Institute for Network Science. She told me she might have to “escape” back to the U.S. before the ban was reinstated or she could be stranded in Canada.

Huddled around a workspace outside the conference rooms, we looked online to learn more. It appeared people with “bona fide” American connections would be given a waiver and allowed entry to the U.S. But it wasn’t clear what that entailed.

Salehi had to make a decision based on facts, and yet the more we searched, the less we felt we knew about what was going on. Salehi called her lawyer. She also called Yale University’s Office of International Students and Scholars. No one knew what was going on—a commonplace happening in Trump’s America.

She booked a flight that departed a few hours later, her opportunity to learn and network at the conference cut short. Other Iranians did the same, many missed talks and opportunities to teach the remaining attendees about their work—a lose–lose.

The day after, our lab met for diner and we talked about Salehi. Scientists don’t talk much about policy; perhaps because it seems like an esoteric Game of Thrones played by politicians, more fodder for caricature than actual engagement. But this wasn’t esoteric for us—one of our crew was missing.

That Salehi traveled 6,000 miles to work at Yale reflects decades of U.S. investment in higher education and research. According to Pew Trusts, half of the U.S. Department of Education’s annual budget, $65 billion (excluding loan programs), is devoted to higher education. Other federal agencies such as the departments of Veterans Affairs and of Health and Human Services, along with the National Science Foundation, the National Institutes of Health, NASA and others contribute to the pie.

Private institutions—the universities themselves—invest billions of dollars each year on research projects and infrastructure. The goal is to build and maintain world-class institutions of learning that attract the world’s brightest minds so they can work together and solve our largest problems.

The motivation is obvious: Science draws on an international economy of brains. The more brains we have, the better; the more diverse those brains, the better. Uniformity is antithetical to science.

After Trump’s first failed travel ban, my wife and I invited Salehi over for tea—as much a sign of solidarity as us seizing the perhaps vanishing moment to learn her story. I’d seen Salehi proselytize the virtues of machine learning; how she actively slows her thoughts to keep pace with her tongue. But I didn’t know her story. Over tea, she told us she hails from a comfortable Tehran apartment, the daughter of a telecommunications engineer and a high school math teacher—both college educated.

Iran maintains separate primary and secondary schools for girls and boys, a requirement of an Islamic government easing into modernized education. She didn’t feel this disadvantaged her at all. (My wife, incidentally, attended a Detroit all-girls private school until college.) Salehi crushed Iran’s college entrance exam and landed a spot at the Sharif University of Technology, Iran’s M.I.T.

By day, she attended class, haunted the library. By night, she dreamt about jobs at data science meccas like Google or Microsoft. Such opportunities can’t be had in Iran because of sanctions don’t allow these companies to have headquarters in Iran. “That’s why many of us come here,” she told me, making here sound like the Emerald City.

Two years ago Iran and the U.S., along with five other nations and the E.U., signed the Joint Comprehensive Plan of Action. In this plan Iran agreed to freeze portions of their nuclear plan in exchange for decreased economic sanctions. “My friends and I were really hopeful that this would help us,” Salehi said. “Especially right now, there are a lot of start-up companies growing in Iran. I myself was thinking about having a start-up. If things are going to get better in Iran, I’m so willing to help build the industry that is in its earliest stages. I was really hopeful.”

Even before Trump’s ban, the travel situation was dire. Like many immigrants and workers—here legally—Salehi hasn't seen her family in years. She doesn't go home for fear of not being able to return.

The dance was foreign to me: For Salehi to visit her family, she has to request a reentry visa. But she can’t do this while in the U.S., and there hasn’t been an American embassy in Iran since diplomatic relations were severed in 1979. So to visit her family, she has to first leave the U.S. then request a return visa from another nation (the most popular is Canada) with a U.S. embassy. Once the application is in, she would visit her family. “This is so stressful,” she told me with a nervous laugh, “I have friends that have been stuck in Iran. The entire month you’re with your family and the U.S. government doesn’t respond, the stress builds.” She had planned her first trip home this August.

I was shocked that my government does this. “I’ve never thought about it any other way,” she shrugged. “It’s the way it is.”

Salehi is part of a large, educated, liberal segment of Iranians whose value system allies with, really mirrors my own as a white MD/PhD. Policies like blanket bans paired with inflammatory rhetoric marginalize these, our colleagues.

As Stephen D. Reicher and S. Alexander Haslam recently explored in Scientific American MIND, studies (theirs and others’) have shown that polarized dialogue is the food of radicalization, which does not happen in a vacuum but feeds on rifts that extremists create, exploit and exacerbate. If you can provoke enough non-Muslims to treat all Muslims with fear and hostility, Reicher and Haslam observed, then those Muslims who previously shunned conflict may begin to feel marginalized and heed the call of the more radical voices among them.

And Trump continues to radicalize and marginalize in just this way. Questions of peace and security cannot be answered with instruments of terror, the very social and military violence that fuels us-versus-them rhetoric.

It is haunting to watch the Trump administration actively sew the seeds of extremism, how their bellicose “crystal ball” policies shove us toward well-studied conclusions.

There has been a march for science, appropriate activism to maintain the U.S.’s scientific leadership and ability to support leading minds. Perhaps we need a march for scientists, for our colleagues who are being threatened under the guise of national security. In the absence of action, there may soon be more empty seats at lab dinners.