During the campaign, Barack Obama hinted at how his future Administration might act to stop suffering in the world.

American foreign policy should focus on more than just killing terrorists; it needs to address "challenges of the 21st century” such as "climate change and poverty, genocide and disease.”

Obama and his advisers all but called for Robert Mugabe’s removal in Zimbabwe and advocated more aggressive U.S. action to halt the genocide in Darfur.

"When genocide is happening,” said candidate Obama during the second presidential debate, "when ethnic cleansing is happening somewhere around the world and we stand idly by, that diminishes us.”

The emerging Obama doctrine seemed to signal a new age of liberal interventionism — the idea that the U.S. has a right and obligation to intervene, by force if necessary, to protect civilians from war and ethnic violence, even in places where the U.S. has no vital national interests at stake.

That doctrine is being tested today in Sri Lanka. And unlike Darfur, where the most egregious crimes were committed long before the current Administration took office, the humanitarian disaster in Sri Lanka has unfolded within the past 100 days, on Obama’s watch.

The Sri Lankan army’s most recent assault on the rebel Liberation Tigers of Tamil Elam (LTTE) has all but wiped out the militants, but at an epic cost to the Tamil population.

At least 50,000 Tamils remain trapped on a two-mile-wide sliver of land, blocked from leaving by rebel fighters, who have used the civilians as shields, and targeted by government forces, who have shelled hospitals, shelters and refugee camps with impunity.

Hospitals are overrun with victims. Scores of children have had limbs amputated to survive. Though it claims to be protecting civilians, the government has blocked the delivery of outside humanitarian aid to the combat zone.

Over the weekend, a doctor there reported that 300 to 1,000 civilians were killed in a single night of shelling, though the government disputes the figures. The death toll in Sri Lanka is unlikely to reach the levels seen in Darfur or Rwanda, but only because there aren’t as many people to kill.

By the standard unanimously adopted by the U.N. General Assembly in 2005, the targeting of Tamil civilians — and the unwillingness of either side to protect them — justifies foreign intervention.

The Responsibility to Protect convention obligates U.N. member-states to step in if "national authorities manifestly fail to protect their populations from genocide, war crimes, ethnic cleansing and crimes against humanity.” That’s an apt description of what’s happening in Sri Lanka.

So why has the situation failed to trigger louder calls to action? Several factors make Sri Lanka an inconvenient place to apply the principles of liberal interventionism.

First, the Sri Lankan government has successfully cast its campaign against Tamil separatists as of a piece with the U.S.-led war on terrorism; the Tigers invented suicide bombing and have until recently continued to target civilians in Sri Lanka’s capital, Colombo.

Second, the civil war between Sri Lanka’s Sinhalese majority and the LTTE has lasted 25 years and already claimed 70,000 lives. The world tends to view long-running civil wars as intractable and impervious to foreign intervention; only when both sides exhaust themselves, the thinking goes, can such wars be stopped.

But the most vexing problem for interventionists is that in Sri Lanka, atrocities against civilians have manifestly been committed by both government forces and the rebels. There are no good guys.

Liberal interventionism works better in theory than in practice. No sovereign government accedes readily to foreign meddling in its own affairs, and liberals remain more reluctant than neoconservatives to insist on a moral right to intervene.

Well-meaning "never again” resolutions like the Responsibility to Protect have too often been shown to be empty gestures, since they are so rarely backed up by action.

That paralysis has been evident in the Obama Administration’s response to Sri Lanka. As the Colombo government’s offensive intensified in April, the Obama Administration condemned both sides for disregarding civilian life — which is the best way to ensure that both continue to do so.

It has since tried to stiffen its language toward the government. Secretary of State Hillary Clinton said "the entire world is disappointed that [the government] is causing such untold suffering.”

On April 29, the U.S. said it would seek to delay a $1.9 billion loan from the International Monetary Fund to Colombo until the government took steps to alleviate civilian suffering.

None of it, though, managed to stop what the U.N. described as a "bloodbath” against the Tamil population over the weekend. And yet in response, the State Department reverted to its pox-on-all-your-houses neutrality.

"We think that there’s an unacceptably high level of civilian casualties,” said spokesman Ian Kelly on May 11. "We’ve repeatedly urged the Tamil Tigers to lay down its arms and allow the civilians to leave the safe zone.

The government of Sri Lanka should abide by its April 27 statement that combat operations have concluded and that — and security forces should end the use of heavy weapons, which, of course, could cause civilian casualties.”

What more can be done? Plenty, actually. The U.S. could press for a U.N. Security Council resolution demanding that government forces adhere to a cease-fire and allow for the delivery of humanitarian aid.

If that doesn’t work, Washington can lean on India, the country with the most leverage over Colombo, to pressure the Sri Lankan government to halt its offensive. If that doesn’t work, the Administration could impose economic sanctions against Sri Lanka, with whom the U.S. did more than $2 billion in trade last year.

If that doesn’t work, the U.S. could push to create safe havens inside the combat zone monitored by U.N. peacekeeping troops, as exists in the Congo.

Wouldn’t that amount to taking sides in the conflict? Not really — it would merely be balancing the score. The U.S. has already classified the LTTE as a terrorist organization, blocking its assets in the U.S. and making it a crime to provide funds to the group.

We don’t have much more leverage over terrorists. Targeting the government’s interests as well would send the message that so long as the welfare of innocent civilians is ignored by the army and the rebels, both sides will feel pain.

By intervening on behalf of Sri Lanka’s civilians, Obama would do more than just save lives — he could help to save the doctrine of liberal interventionism before it ends up in history’s warehouse of good intentions. Because if he doesn’t do it, who will?

TIME