Northampton, Mass. - Of all the issues President-elect Barack Obama faces before he takes office, none is of greater moral urgency than changing the tenor of the US response to what he has repeatedly described as "genocide in Darfur."

That's because, before Inauguration Day, the International Criminal Court (ICC) is very likely to issue a warrant for the arrest of Sudan's president, Omar al-Bashir, charging him with crimes against humanity and genocide in Darfur.

These charges are amply justified by the evidence. Mr. Obama's clear and effective response is needed, because the Khartoum regime has threatened aggressive violence in a calculated campaign to fend off the arrest.

Indeed, its threats are as shocking as they are underreported.

In August, the UN head of mission in Sudan declared to the Security Council: "The government has conveyed to me that the issuance of an arrest warrant against President Bashir could have serious consequences for UN staff and infrastructure in Sudan." Translation: Seek to arrest our president and we'll unleash further hell on the aid personnel who protect Darfur's vulnerable civilian populations.

Also in August, Bashir declared, "We are ready to go through war with the great power" to forestall ICC actions. Such threats against UN personnel and operations are unprecedented – and they must be fully registered by the Security Council, both for Darfur and for future peacekeeping and humanitarian operations.

As if to make clear just how high the stakes have become, Assistant Secretary-General for Peacekeeping Edmond Mulet recently stressed that a warrant for Bashir could "derail the [north/south] Comprehensive Peace Agreement," which in January 2005 ended more than 20 years of catastrophic civil war.

Sudan's unambiguous threat – which also poses grave regional dangers – means the international community has no excuse not to act forcefully now. And yet, to date, Khartoum's threats stand unrebuked. The UN Secretariat has acquiesced: Despite Secretary-General Moon's tepid and abstract support for the ICC, he refuses to challenge Khartoum directly over its recent dangerous pronouncements.

Compounding the diplomatic problem, several regional organizations and international groups are pushing for deferral of any indictment of al-Bashir – not because of doubts about his guilt, but in service of a putative "Darfur Peace Process."

But no such process exists or lies in prospect, primarily because no adequate pressure exists on Khartoum to engage meaningfully.

Perversely, present efforts on Bashir's behalf by the Arab League, the African Union, and the Organization of the Islamic Conference work to sustain Khartoum's sense of impunity rather than create the necessary pressures for radical changes in regime behavior on the ground throughout Darfur – the key to any meaningful peace agreement.

That's why the "peace versus justice" trope often invoked by Westerners is the wrong way to think about Darfur. It's not a choice between peace and justice, not if we are serious about meaningful peace: for it is precisely the relentless absence of justice and accountability (impunity) that has sustained violence in Darfur and will continue to do so if unaddressed.

What will follow if an Obama administration, its Western and democratic allies, and a divided Security Council allow Khartoum to make good on its ominous threats?

After more than five years of genocidal counterinsurgency war, hundreds of thousands have died. Around 4.7 million civilians in Darfur remain affected by the conflict and in need of humanitarian assistance; nearly 3 million have been displaced from their homes, and approximately the same number need food aid.

The fragile lifeline of assistance simply cannot continue without greater protection of the sort promised by the UN-authorized peacekeeping force known as UNAMID. Yet now Khartoum is threatening UNAMID militarily and the tenuous security it provides to the world's largest and most endangered aid operation.

The Obama administration can take a key leadership role right now, beginning with unambiguous support for the international legitimacy of the ICC. The administration in waiting should also commit to the provision of critical helicopter and ground transport, the lack of which has so far crippled UNAMID.

The European Union must be pressed vigorously to impose monetary sanctions. Heavy diplomatic pressure must be exerted on China, Sudan's most powerful ally, to condemn all threats against the UN.

And the US must be sharply mindful of Khartoum's evasive penchant for engaging multiple diplomatic interlocutors: With its regional and global allies, the US must work to compel the regime to engage with a single, credible peace forum that recognizes not only Darfuri combatants and civil society leadership, but the obligations of international law.

To do less is to acquiesce to the threats of a brutal regime whose responsibility for atrocity crimes throughout Darfur is beyond dispute.

• Eric Reeves is author of "A Long Day's Dying: Critical Moments in the Darfur Genocide.