Behind-the-scenes U.S. pressure has finally forced Iraq's leaders to accept a political compromise, with Sunday's vote in the Iraqi parliament to adopt an electoral law setting rules for national elections in January — and potentially clearing the path to withdrawal for tens of thousands of U.S. troops.The vote had been delayed for weeks over the apparently parochial issue of electoral lists for the contested northern city of Kirkuk. Oil-rich Kirkuk, claimed by Iraq's Kurds as an integral part of their autonomous semistate but administered by the Arab-dominated government in Baghdad, has long been a potential flash point in the uneasy relationship between the Kurdish autonomous region and Baghdad. Sunday's compromise, which allows recent Kurdish returnees (much of the city's Kurdish population had been expelled by Saddam Hussein, precisely to cement Arab control there) to vote in Kirkuk but gives parliament the authority to investigate any suspicious voting patterns, came only after strong pressure from U.S. Vice President Joe Biden, who made personal phone calls to top Kurdish leaders while the U.S. ambassador counted Arab votes in Baghdad. But while it smooths the way for January's elections, the deal does not address the status of Kirkuk, which will remain one of the most difficult questions confronting Iraq's next government.Ever since the U.S. invasion of Iraq, observers have viewed Kirkuk, which is coveted by Kurds, Turkomans and Arabs, as a potential trip wire for civil war. The fact that it has remained largely stable owes much to the cosmopolitan character of the city's native population, and the city's heroic local police force led by three generals — a Kurd, an Arab and a Turkoman. The relative calm in Kirkuk may also be a vindication of the Baghdad government's foot-dragging over the question of whether to turn Kirkuk over to Kurdish control.Iraqi Prime Minister Nouri al-Maliki pledged to abide by the Iraqi constitution and "normalize" Kirkuk by removing the tens of thousands of Arab Iraqis settled there by Saddam as part of an ethnic-cleansing campaign in the 1980s. After such normalization, according to the constitution, Kirkuk — and other areas with large Kurdish populations in four Iraqi governorates — should then hold a referendum to determine whether they should continue to be administered by Baghdad or be ruled by the Kurdistan Regional Government. It may have been constitutionally mandated, but the idea of forcibly resettling Kirkuk's Arab population was unthinkable while Iraq was in the grip of a Sunni-Arab insurgency and a Shi'ite-Sunni civil war, and that became the excuse for the al-Maliki government to allow several referendum deadlines to pass.Iraq's improving security situation has eliminated many of the excuses for postponing the normalization process in Kirkuk envisaged by the constitution, and Kurdish politicians have begun to suspect that al-Maliki intends to use the central government's growing strength to push back against gains won by the Kurds in the aftermath of the invasion, when the government in Baghdad was weak. The central government has already blocked oil pumped under the auspices of the Kurdish regional government from being exported in Iraqi pipelines, even though revenue from the sales would have been shared with the central government.So, as the other security challenges become more manageable, the Arab-Kurd fault line in Kirkuk has become increasingly dangerous. Such is the enmity between the two leaders that al-Maliki and Kurdish Regional Government President Masoud Barzani rarely speak to each other. Iraqi troops and the Kurdish Pesh Merga have clashed several times in disputed areas in recent months, forcing U.S. officers to mediate to avoid escalation.All sides recognize that with U.S. troops preparing to depart under a Status of Forces Agreement with the Iraqi government that requires that their withdrawal be completed by the end of 2011 (and the demands of the Afghanistan war requiring that many leave even sooner), the future of Arab-Kurdish relations could be substantially shaped by the composition of the next government. The Kurds have played a kingmaking role in the democratic process since Saddam's ouster, but their backing for the Shi'ite-dominated al-Maliki government in 2005 did little to cement Kurdish territorial claims. But now that Sunni Arabs no longer boycott elections, Kurdish parliamentary influence will be diminished. Indeed, stiffening resistance to Kurdish political demands could be a key point of consensus in any Sunni-Shi'ite political alliance that emerges after the elections — and that could make Kirkuk's relative stability a thing of the past.