In late March 2011, as a hopeful Arab Spring unfolded haltingly across the Middle East and North Africa, President Obama spoke triumphantly about a new moral direction for the use of military force in defense of human rights.

His subject was Libya, where his administration had intervened with European and Arab nations to protect a rebel uprising from a resurgent Libyan army and a massacre threatened by dictator Moammar Gaddafi.

“To brush aside America’s responsibility as a leader and — more profoundly — our responsibilities to our fellow human beings under such circumstances would have been a betrayal of who we are,” Obama said. “Some nations may be able to turn a blind eye to atrocities in other countries. The United States of America is different.”

In the same month, Syria’s civil war began in the small southern border city of Daraa, where government forces moved violently to end weeks of protest. More than 140,000 Syrians have been killed since then in a country Obama acknowledged last week is “crumbling.”

The moment offers a vivid hindsight view of a president’s words and actions colliding with national security implications, as the Syrian conflict approaches a grim third anniversary.

Just how different is the United States under Obama? The question holds fresh urgency as the peace process stagnates and the Syrian government employs new methods of barbarity. Recent administration warnings that the distant war poses a direct threat to the United States have elevated Syria, and Obama’s stated principles for intervention, to the top of a crowded national security agenda.

On Wednesday, Obama warned Ukraine’s government, also the target of broad popular protests, not to “step over the line” in its move against demonstrators, threatening international reprisals if it does. The punishment would most likely be sanctions, but the threat again puts on the line the president’s credibility to carry through with pledges to protect anti-government protesters.

Obama has no election ahead, as he did when he intervened in Libya, only a presidential legacy to consider. He is the president who is unwinding the United States’s post-9/11 conflicts. With the U.S. combat role in the Afghanistan war scheduled to conclude at the end of the year, the goal may be too close to start a new one.

The question Obama and his advisers confront is whether his inaction in Syria — beyond diplomacy and humanitarian help — will come to define his legacy more than his action in Libya. Nearly half of Americans, including many Democrats, already disapprove of his handling of Syria’s war.

“The search for the perfect option has become the enemy of options that would help us manage the situation far better than we are,” said one American human rights advocate, who spoke on the condition of anonymity to candidly discuss administration policy.

“There are certainly no good options in Syria,” this person said. “But the question is, are there things we could do in Syria that would leave us better off? When he was asked that question two years ago, the answer was no. But in hindsight, maybe it should have been — and still continues to be — yes.”

The speech the president delivered on the evening of March 28, 2011, was immediately identified as an example of an “Obama Doctrine,” after the studied pragmatism that marked his early foreign policy initiatives. The approach stood in contrast to the ideologically charged George W. Bush years, a period during which Obama has said the country “lost its way.”

He laid out three main principles for intervention: an imminent humanitarian catastrophe, international support and a limited operation in pursuit of a vital national security interest. They were meant to stand as a logical framework that was lacking when the United States invaded Iraq, which Obama called “a dumb war.”

The situations in Syria and Libya, and the international diplomacy surrounding each, are distinct. But the Libya intervention was, in some important ways, the military solution that Obama and his senior advisers now say does not exist in Syria.

Russia’s opposition to another U.S.-led military operation in the region makes U.N. support — key to Obama’s decision last time — impossible to secure now.

The Arab League is also divided in a way that it wasn’t during the Libya conflict over what rebel faction to support. Gaddafi, unlike Syrian President Bashar al-Assad, had nearly no international support. The fledgling peace process in Geneva is in limbo and going nowhere.

“The progress has been frustratingly slow, there’s no question about it,” White House press secretary Jay Carney said this week. “But it does not change the central fact that in our view there is not a military resolution to this conflict.”

But in Syria’s war, where virtually no distinction is made between soldier and civilian, the humanitarian threat is far worse than the one that prompted U.S.-led action in Libya at a time when several hundred Libyans had been killed.

The war’s contours also are shifting more in line with the principles for intervention that Obama laid out three years ago, including a growing threat of a government victory in key rebel areas and a rising national security risk to the United States.

After months of bombarding the rebellious city of Aleppo, Syria’s army is beginning to move against it on the ground. Government helicopters are dropping improvised “barrel bombs” on civilians in the city.

Assad has not threatened the population publicly, as Gaddafi did as he moved on Benghazi. But the Syrian president has already brazenly crossed Obama’s “red line” by killing more than 1,500 civilians, including hundreds of children, with poison gas during the course of the war. And there is a growing national security concern, as Syria’s battlefield grows more chaotic.

Earlier this month, Homeland Security Secretary Jeh Johnson, in his first policy address in the job, said that “Syria has become a matter of homeland security.”

He was referring to the exodus of trained foreign fighters from Syria, including from the ranks of the hard-line Islamist factions once allied with al-Qaeda, making their way into Europe and perhaps the United States. Obama noted last week that the Islamists were undermining “global national security.”

“The moon and the stars are not as aligned diplomatically as they were in Libya,” the human rights advocate said, “but there is a far greater humanitarian and national security interest to act.”

The post-9/11 wars he inherited shadowed Obama’s decision to intervene in Libya, and they are doing the same on Syria. Now, though, Obama can see the end of the wars clearly.

As he noted when announcing the military campaign in Libya, “At a time when our military is fighting in Afghanistan and winding down our activities in Iraq, that decision is made only more difficult.”

Syria’s battlefield, now featuring a deeply divided rebel force, has also grown more complicated in recent months. The distinction between ally and enemy — of the United States and of each other — is nearly indiscernible.

A frustrated Obama has chosen to increase humanitarian aid — and expand a rebel covert training program run by the CIA — rather than enter the conflict directly. The window for what Obama envisioned as a military solution, or at least a role for military pressure, has in the eyes of administration officials closed for now.

“It’s very uncertain whether arming the rebels would have the desired effect or whether airstrikes would have the desired effect, and this has contributed to an understandably cautious approach from the international community, our own government included,” said Michael Abramowitz, director of the Center for the Prevention of Genocide at the U.S. Holocaust Memorial Museum, who returned this week from a visit to Syria’s border with Jordan.

“But basically you have a situation now where unless something changes the calculus of the battlefield, then thousands more are going to die or be displaced,” Abramowitz added. “And I say that without knowing what that action is.”

Last fall, after the second confirmed use of chemical weapons in Syria, Obama saw an opportunity for military force and threatened airstrikes across Syria. He believed intervention would worsen the humanitarian situation, but he worried even more about Assad’s weapons of mass destruction, as did the Israelis.

A senior administration official involved in Syria policy said at the time that Obama “comes at this less as a humanitarian intervention, and more from his more nonproliferation perspective.”

“Our national security is implicated by the fact that this is the introduction of chemical weapons to a battlefield in a region where there are many U.S. interests intersecting on the ground,” the official said.

But Obama put the final decision in the hands of Congress, whose members had little appetite for the fight. Then Assad agreed, under Russian pressure, to give up his chemical arsenal, a process that has yet to be fulfilled.

At the time of the Libya conflict, the liberal interventionists within Obama’s administration helped persuade him to assert U.S. power to prevent, in his words, “a massacre that would have reverberated across the region and stained the conscience of the world.”

Chief among them were Susan Rice and Samantha Power, who have since been promoted to national security adviser and U.S. ambassador to the United Nations, respectively.

Both have condemned Assad’s actions, and in recent weeks the debate within the administration over a more assertive policy, led by Secretary of State John F. Kerry and supported by Power, has intensified.

Yet the argument for direct military intervention remains far more muted in the West Wing than it was three years ago. Addressing the nation, Obama said then that there will be times “when our safety is not directly threatened, but our interests and our values are.”

“These may not be America’s problems alone,” he said. “But they are important to us. They’re problems worth solving.”