Barack Obama's tone of mild exasperation when tutoring the public often makes his pronouncements grating even when they are sensible. As was his recent suggestion that Americans, misled by media, are exaggerating the threat of terrorism.

The world might currently seem unusually disorderly, but it can be so without being unusually dangerous. If we measure danger by the risk of violence, the world is unusually safe. For this and other reasons, Americans should curb their pessimism.

The Washington Post's Anne Applebaum recently reminded readers that in three decades of terror the Irish Republican Army murdered more than 2,000. And Italy's Red Brigades committed many attacks, killings and kidnappings. Both groups had foreign support. The Islamic State group is dangerous, but the West has faced, and surmounted, worse. The Islamic State poses neither an existential threat nor even a serious threat to the social cohesion or functioning of any developed nation.