Obama addresses nation on Syria U.S. President Barack Obama addresses the nation about the situation in Syria from the East Room at the White House in Washington, September 10, 2013. (Reuters/Evan Vucci)

President Obama needed to do two things in his Tuesday night speech on Syria. He did one well.

Obama offered a stirring moral case that American foreign policy is at its noblest when it defends not only our national security but also universal values.

When dictators commit atrocities, they depend upon the world to look the other way until those horrifying pictures fade from memory. But these things happened. The facts cannot be denied. The question now is what the United States of America and the international community is prepared to do about it. . . .

The burdens of leadership are often heavy, but the world’s a better place because we have borne them. And so to my friends on the right, I ask you to reconcile your commitment to America’s military might with the failure to act when a cause is so plainly just.

To my friends on the left, I ask you to reconcile your belief in freedom and dignity for all people with those images of children writhing in pain and going still on a cold hospital floor, for sometimes resolutions and statements of condemnation are simply not enough. . . .

Franklin Roosevelt once said, “Our national determination to keep free of foreign wars and foreign entanglements cannot prevent us from feeling deep concern when ideas and principles that we have cherished are challenged.”

“Our ideals and principles,” the president concluded, “are at stake in Syria.”

The president is right that America runs a danger if it fails to do something meaningful: that a mighty nation will have to suffer the moral stain of doing little in the face of large-scale and disgusting humanitarian abuse. Obama wants to make it clear that mass murderers will pay a price for extreme brutality, even if America can’t respond to every outrage across the planet.

But we should also have a clearer sense of how the United States will approach the larger Syrian conflict, which had already resulted in 100,000 deaths before the latest gas attacks, along with an explanation of whether and why it matters to the United States, morally or strategically.

Many Americans might accept the justice of the president’s cause but still object that he does not seem to have a strong sense of how it would interact with a broader policy in the region. Obama insisted that American strikes would harm Syrian President Bashar al-Assad’s regime, but also that “we cannot resolve someone else’s civil war through force.”

So how does he see this ending, after the commitment of American resources?