Had one of Donald Trump’s Republican opponents during the campaign for the GOP nomination given the same speech on combating global terrorism he gave last week, it would have raised few eyebrows. Naturally, competing candidates would have disputed particular points—some vigorously—but the speech’s overall analysis fits well within mainstream conservative and Republican thinking.

Some Trump opponents and supporters alike will be distressed by this news, but the speech visibly sharpens the contradictions with Hillary Clinton,...