The facade of the Nador street building of Central European University in Budapest. (Zsolt Szigetvary/EPA-EFE/Shutterstock)

THE IRON CURTAIN was a notion but also a reality: Freedoms were respected and common in the West, and extinguished under all-powerful parties and strongmen in the East, in the nations of the Soviet bloc. When the division of Europe disappeared between 1989 and 1991, many exulted in the opportunity for democratic values to reach lands where they had been so long denied. This was the fundamental promise of Central European University, an institution that would propagate openness and rule of law, based in a transformed Hungary, now a member of NATO and the European Union.

The graduate school, founded and financed by philanthropist and financier George Soros, became a respected outpost for thousands of students to focus on “open minds and open frontiers,” as the president and rector, Michael Ignatieff, once put it. On Monday, the university became a casualty of a new Iron Curtain falling across the democratic world, in this case led by Hungarian Prime Minister Viktor Orban, an autocratic nationalist who has vilified Mr. Soros and waged a long campaign to oust CEU from Budapest. The university announced it had been “forced out” of Hungary, in “a flagrant violation of academic freedom,” a shattering blow to the ideals that led to the university’s founding. Planning to relocate programs to Vienna, the university declared, “It is a dark day for Europe and a dark day for Hungary.”

It was also a dark day for U.S. diplomacy and its traditional support for democratic values, now an occasional afterthought for the Trump administration. The State Department said the United States had “worked diligently” for a compromise that would allow CEU to remain in Hungary. As The Post’s Griff Witte reported last week, the U.S. ambassador to Hungary, David B. Cornstein, an 80-year-old New Yorker who made a fortune in the jewelry, gambling and telemarketing industries, and who boasts of a longtime friendship with President Trump, initially tried to push Hungary for a compromise. But Mr. Orban rebuffed his efforts — at which point t he ambassador obtusely described the conflict as little more than a grudge match between Mr. Orban and Mr. Soros. “It had to do with two men,” Mr. Cornstein said. “It doesn’t have anything to do with academic freedom.” Then, he perniciously cast the blame on Mr. Soros, comparing the university’s situation to his experience owning jewelry shops within a department store. “I was a guest in another guy’s store,” he said. “The university is in another country. It would pay to work with the government.”

This is entirely misguided. The ouster of the university is a matter of principle, a major setback for democracy at a time when autocrats such as Mr. Orban are on the march, smothering freedoms and the organizations, such as CEU, that are so vital in keeping the flame alive for this and future generations.