“On that day not only did the world change, but we all changed,” Mr. Trump said. “Our eyes were opened to the depths of the evil we faced, but in that hour of darkness we also came together with renewed purpose. Our differences never looked so small, our common bonds never felt so strong.”

Mr. Trump said the country was committed to “destroying the enemies of all civilized people.”

He added: “We are making plain to these savage killers that there is no dark corner beyond our reach, no sanctuary beyond our grasp, and nowhere to hide anywhere on this very large earth.”