“Viktor Orbán has done a tremendous job in so many different ways,” said President Trump as he received Hungary’s prime minister in the Oval Office Monday. “Respected all over Europe. Probably, like me, a little bit controversial, but that’s OK.” With these remarks, the U.S. president gave his seal of approval to Europe’s leading illiberal politician less than two weeks before elections for the European Parliament.

David Cornstein, the U.S. ambassador to Hungary and a personal friend of Mr. Trump, remarked in a recent interview:...