But Americans benefit, perhaps more than anyone else, from the leading role the country plays in the world. The task of U.S. leaders is to remind the people that we have a lot to lose if others come to believe that we are no longer willing to bear the burdens of leadership…

Syria is about more than our interests, narrowly construed. What we do now is “profoundly about who we are,” as Mr. Kerry put it. “We are the country that has tried, not always successfully, but always tried to honor a set of universal values around which we have organized our lives and our aspirations. This crime against conscience, this crime against humanity, this crime against the most fundamental principles of international community, against the norm of the international community—this matters to us, and it matters to who we are. And it matters to leadership and to our credibility in the world.”

Mr. Obama will need to convey this idea to the American people as well, from the Oval Office. He must be prepared to go all-in to win what is shaping up as a tough fight on Capitol Hill. One thing is clear: A loss would shatter his presidency, and a lot more.