AP Photo

FIFTEEN years ago today, the bombing of the Alfred P. Murrah Building in Oklahoma City claimed the lives of 168 men, women and children. It was, until 9/11, the worst terrorist attack in United States history. But what emerged in its aftermath — the compassion, caring and love that countless Americans from all walks of life extended to the victims and their families — was a powerful testament to the best of America. And its lessons are as important now as they were then.

Most of the people killed that day were employees of the federal government. They were men and women who had devoted their careers to helping the elderly and disabled, supporting our veterans and enforcing our laws. They were good neighbors and good friends. One of them, a Secret Service agent...