By Sam Tabahriti, Charlotte Van Campenhout and Anna Dittrich LONDON/AMSTERDAM/HEMHOFEN, Germany (Reuters) -Thousands of foreign students at Harvard University were stuck in administrative limbo and looking for alternatives on Friday after U.

WASHINGTON (AP) — Harvard University is challenging the Trump administration’s decision to bar the Ivy League school from enrolling foreign students, calling it unconstitutional retaliation for defying the White House’s political demands.

Harvard University can no longer enroll foreign students, the Department of Homeland Security said Thursday, escalating the Trump administration's efforts to exert influence over the Ivy League school.