Fifteen years ago this week, Colin Powell, then the secretary of state, spoke at the United Nations to sell pre-emptive war with Iraq. As his chief of staff, I helped Secretary Powell paint a clear picture that war was the only choice, that when “we confront a regime that harbors ambitions for regional domination, hides weapons of mass destruction and provides haven and active support for terrorists, we are not confronting the past, we are confronting the present. And unless we act, we are confronting an even more frightening future.”

Following Mr. Powell’s presentation on that cold day, I considered what we had done. At the moment, I thought all our work was for naught — and despite his efforts we did not gain substantial international buy-in. But polls later that day and week demonstrated he did convince many Americans. I knew that was why he was chosen to make the presentation in the first place: his standing with the American people was more solid than that of any other member of the Bush administration.