Across Turkey’s southern border, Bashar Assad’s criminal regime has for seven years targeted Syria’s citizens with arbitrary arrests, systematic torture, summary executions, barrel bombs, and chemical and conventional weapons. As a result of the Syrian civil war, which the United Nations Human Rights Council calls “the worst man-made disaster since World War II,” millions of innocent people have become refugees or been internally displaced.

Turkey has gone to extraordinary lengths to alleviate suffering of the Syrian people,...