What propels Islamist terrorism and attacks against France is more than an academic debate: The answer shapes policy toward blunting the threat. So it is no inconsequential matter in a culture under attack, and one that so cherishes its intellectual debates, that France’s two leading scholars of radical Islam — former friends — have turned bitter rivals over their differing views.

These skeptical analysts argue that many current messaging strategies against the Islamic State are backfiring — and that polarizing politicians such as Trump have amplified the jihadists’ impact and been their best recruiting tool. Islamophobia helps the jihadists by fueling their narrative about embattled Muslims, Kenning argues. It creates a sense of wounded community — a shared identity of having been wronged, which prompts violent revenge.