Bernie Sanders Falls Behind in a Race Centered on Security

In his opening remarks at the Democratic presidential debate on Saturday, Senator Bernie Sanders railed against “establishment politics and establishment economics” and then the nation’s “rigged economy.” He moved on to the “corrupt” campaign finance system, then the “planetary crisis of climate change.” Only after that did he say he wanted to destroy the Islamic State.

It was a litany of priorities that made good sense when Mr. Sanders announced his presidential bid in April. But after the terrorist attacks in Paris and San Bernardino, Calif., he made fighting terrorism...