After future doctors finish medical school, they go on to residency programs to wrap up their training in hospitals. Both American and foreign medical-school graduates can apply to American residency slots, and among this year’s foreign applicants, there are currently 260 people from the seven nations—Iraq, Syria, Iran, Libya, Somalia, Sudan, and Yemen—banned from coming to the U.S. for 90 days under President Trump’s executive order, according to the Association of American Medical Colleges.

Because the total number of residency slots are limited, many of these individuals might not become American doctors. The typical primary-care doctor sees 3,000 patients, so the AAMC is estimating those 260 future doctors would have been able to take care of more than three-quarters of a million American patients.

Foreign medical students typically come to the U.S. under J1 or H1 visitors’ visas, which are subject to Trump’s 90-day ban. Residency matching typically happens in March, and residents start in June. That’s more than 90 days away, but “the uncertainty is throwing people off,” said Atul Grover, the director of the AAMC, which oversees the residency matching program.

“The program directors are like, ‘what do I do?’” Grover told me. “If there’s someone who I think is going to make a fantastic doctor from Sudan, are we going to be able to take them?”

Only foreign medical graduates whose colleges are recognized by the U.S. and who pass U.S. qualifying exams are eligible to apply for American residencies. Typically, only half of all foreign medical students secure an American residency spot, so the true number of potential future doctors who would be excluded from the program is around 130. Still, those people would have been able to take care of nearly 400,000 Americans upon graduation.

As a twist, it’s the most needy Americans who will lose out if the doctors are barred from entry. There’s a major shortage of doctors, even though nearly a quarter of all practicing American physicians are foreign-educated, Grover said. One way foreign medical graduates can negotiate to stay in the U.S. after their residency is through a visa waiver under which they agree to practice in underserved areas for several years. That’s why some studies estimate that foreign medical graduates are more likely than Americans to work in these doctor deserts.

Grover said residency program directors are still frantically trying to sort out the rules, but in some ways, the chilling effect has already begun. As ProPublica reported over the weekend, one Cleveland-Clinic medical resident who had a Sudanese passport was forced to return to Saudi Arabia hours after her plane landed in New York.

“I’m only in this country to be a doctor, to work and to help people — that’s it,” the woman, Suha Abushamma, told ProPublica. “There’s no other reason.”