A clumsy European Union has repeatedly gotten its policy toward Turkey wrong, often inadvertently helping President Recep Tayyip Erdogan at key points during his rise. Mr. Erdogan may now be eyeing snap elections, putting Europe in a bind. Brussels would be forced to look the other way as the new sultan bulldozes his way to victory in the polls.

When Mr. Erdogan’s Justice and Development Party, known by the Turkish initials AKP, came to power in 2002, the EU failed to grasp the nature of the party’s limited mandate. Turkey’s...