WASHINGTON (AP) — A federal judge has temporarily blocked a proclamation by President Donald Trump that banned foreign students from entering the U.S. to attend Harvard University.

Trump's proclamation was the latest attempt by his Republican administration to prevent the nation’s oldest and wealthiest college from enrolling a quarter of its students, who account for much of its research and scholarship.

Harvard filed a legal challenge on Thursday, asking for a judge to block Trump’s order and calling it illegal retaliation for Harvard’s rejection of White House demands. Harvard said the president was attempting an end-run around a previous court order.

A few hours later, U.S. District Judge Allison Burroughs in Boston issued a temporary restraining order against Trump’s proclamation. Harvard, she said, had demonstrated it would sustain “immediate and irreparable injury” before she would have an opportunity to hear from the parties in the lawsuit.

Burroughs also extended the temporary hold she placed on the administration's previous attempt to end Harvard's enrollment of international students. Last month, the Department of Homeland Security revoked Harvard's certification to host foreign students and issue paperwork to them for their visas, only to have Burroughs block the action temporarily. Trump’s order this week invoked a different legal authority.

If Trump’s measure were to survive this court challenge, it would block thousands of students who are scheduled to go to Harvard's campus in Cambridge, Massachusetts, for the summer and fall terms.

“Harvard’s more than 7,000 F-1 and J-1 visa holders — and their dependents — have become pawns in the government’s escalating campaign of retaliation,” Harvard wrote Thursday in a court filing.

While the court case proceeds, Harvard is making contingency plans so students and visiting scholars can continue their work at the university, President Alan Garber said in a message to the campus and alumni.

“Each of us is part of a truly global university community,” Garber said Thursday. “We know that the benefits of bringing talented people together from around the world are unique and irreplaceable.”

Harvard has attracted a growing number of the brightest minds from around the world, with international enrollment growing from 11% of the student body three decades ago to 26% today.

As those students wait to find out if they'll be able to attend the university, some are pursuing other options.

Rising international enrollment has made Harvard and other elite colleges uniquely vulnerable to Trump's crackdown on foreign students. Republicans have been seeking to force overhauls of the nation's top colleges, which they see as hotbeds of “woke” and antisemitic viewpoints.

Garber says the university has made changes to combat antisemitism. But Harvard, he said, will not stray from its “core, legally-protected principles,” even after receiving federal ultimatums.

Trump's administration has also taken steps to withhold federal funding from Harvard and other elite colleges that have rejected White House demands related to campus protests, admissions, hiring and more. Harvard's $53 billion endowment allows it to weather the loss of funding for a time, although Garber has warned of “difficult decisions and sacrifices” to come.

But cutting off students and visiting scholars could hamstring the university's research and global standing.

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