In his address in early September regarding a possible strategy against the Islamic State in Iraq and Syria (ISIS), President Obama was keen to stress that the group is “not Islamic.” “The vast majority of ISIL’s victims have been Muslim,” he said, using another acronym by which the group is known. Also, “No religion condones the killing of innocents.” In saying this, President Obama stands in a long line of Western leaders — from both ends of the political spectrum — who have repeated a lie that may finally be falling apart.

For more than a decade, nearly every politician has …