ISIS is creating a zone of instability from the Strait of Gibraltar to Central Asia. This could result in the creation of radical Islamic terror states along the southern Mediterranean and the overthrow of the Western-oriented Egyptian regime, both of which would directly harm U.S. interests.

This same volatility could threaten Israel; undermine our Saudi, Jordanian, and Gulf state allies; and help return the Taliban to power in Afghanistan. It could topple the government of nuclear-armed Pakistan. Radicalization could destabilize the peaceful, largely Western-oriented Muslim nation of Indonesia. The Obama administration seems clueless about ISIS’ catastrophic potential and has no long-term strategy to bend events to America’s benefit.

President Harry Truman, by contrast, thought decades ahead. The haberdasher from Missouri reformed the government to meet new challenges after World War II and created international structures that helped contain America’s adversaries and win the Cold War. Mr. Obama’s vision is limited to the coming months, to the next quarter, to the end of his term. Whenever events undermine his view of the world, he has the habit of retreating to an alternate reality. Mr. Obama is a man with an uncommonly rigid, anti-empirical mind.

We’ve seen this manifest itself in areas other than foreign policy—for example, in his refusal to address the entitlement and debt crises.