WASHINGTON -- For years the Sudanese regime, headed by President Omar Hassan al-Bashir, has acted the part of a terrorist gang, holding millions of refugees in Darfur camps hostage and warning the world not to make any sudden or aggressive moves. Now the world faces a question: What do we do when the captors begin killing their captives?

After the International Criminal Court issued a warrant for his arrest on the charge of crimes against humanity, Bashir responded by expelling 13 international relief groups -- including four key partners of the World Food Program (WFP) responsible for distributing food to 1.1 million people in Darfur. In a stroke, Bashir removed about 35 percent of Darfur's food distribution capacity. And he has hinted that all international aid groups might be thrown out by year's end.

Dr. Mohammed Ahmed Abdalla, a physician and human rights advocate in Darfur, described to me a region "on the verge." Without international aid groups to organize supply, only about 9 percent of people in the camps have access to clean water. There is a serious meningitis outbreak, just as medical aid groups have been expelled. "People," says Mohammed Ahmed, "are likely to die very soon."

Bashir claims that his goal is to "Sudanize" the relief efforts, insisting that the international community can drop off supplies "at airports or seaports" to be distributed by Sudan's regime. "They don't have the technical capacity or the know-how," Mohammed Ahmed counters. "And even if they did, it wouldn't be accepted by the people." It is not realistic to expect the victims of Bashir's genocide to trust in Bashir's generosity. The same is true, Mohammed Ahmed argues, of promised relief from the Arab Middle East. "Darfur will never trust Arab aid. Though they are also Muslims, they have never been helpful. People think such assistance is easily poisoned."

The WFP has responded to the immediate crisis, providing two months of emergency food assistance to the Darfur camps in an attempt to persuade people to stay put. But this effort, I was told by a WFP official, is "not sustainable." So the WFP has also begun positioning food for the possible influx of tens of thousands of desperate refugees into eastern Chad. Mohammed Ahmed views this prospect with horror. "People moving to safety and food security from the Kalma camp (Darfur's largest) to eastern Chad would have to cover 500 kilometers, risking attacks from the Janjaweed and rebels in Chad near the border." It would be a long, dry, lethal march.

The international community, led by the United States, now faces a decision. It might be possible to back down from confrontation with Bashir in the hope that aid groups would be allowed to return. An atmosphere of heightened hostility also complicates the implementation of the peace agreement between Sudan's north and south, on which many lives depend. There is a humanitarian argument for this course. But it would confirm the effectiveness of Bashir's strategy of punishing the innocent and confirm the permanence of a violent and unjust status quo in Darfur.

Or the world can increase the pressure on Sudan's regime, knowing that Bashir may cause more short-term suffering and death as such pressure is applied. This approach can be morally justified only if there is a reasonable hope of eventual success. And this requires the development of a thoughtful strategy that leads, step by step, to a government in Sudan that values the people of Darfur and implements the north-south agreement in good faith. This does not necessarily mean regime change, but it probably requires Bashir change -- the emergence of a Sudanese leadership willing to start anew.

In this task, the Obama administration has two great advantages. The first is Bashir himself, whose unhidden, unhinged brutality is destroying the credibility of all who have shielded him in the past. The second is President Obama's extraordinary global standing, which he could use to persuade Europeans on broader economic sanctions and to peel off traditional Sudanese supporters such as Egypt. But this would require the immediate expenditure of diplomatic capital, the elevation of this issue in relations with both friends and rivals, and the possible use of military force down the road.

Not every global humanitarian crisis justifies this kind of commitment, else America would be endlessly overextended. But if genocide does not justify such action, it will never be justified. And we would lose the right to say, "never again." Michael Gerson's e-mail address is michaelgerson(at)cfr.org. (c) 2009, Washington Post Writers Group