WASHINGTON President Barack Obama's vow to withdraw all U.S. combat troops from Iraq by the end of August will be tested this weekend as millions of Iraqis head to the polls to elect a new government.
While the United States has faced many critical junctures during the seven-year-old Iraq war, arguably the stakes have never been higher than they are now.
If the election goes well, U.S. soldiers can go home on schedule. But, if it triggers a repeat of the sectarian bloodletting that killed tens of thousands of Iraqis in 2006-2007, Obama may be forced to rethink his timetable.
An eruption of violence that threatens Iraq's stability would also be an unwelcome distraction for Obama, who has declared that bringing down the United States' stubbornly high unemployment rate will be his top priority this year.
He left himself little wiggle room in his State of the Union address to the American people in January.
"We will have all of our combat troops out of Iraq by the end of this August," he said. "Make no mistake: this war is ending, and all of our troops are coming home."
Obama campaigned on a promise to bring a swift end to a war that has claimed the lives of more than 4,300 U.S. soldiers and drained the U.S. Treasury of hundreds of billions of dollars.
With an economy only starting to recover from recession and a deteriorating security situation in Afghanistan, the Iraq war has not been a top priority for Obama, although he has appointed his vice president, Joe Biden, to manage it.
Now, however, Obama has arrived at his moment of truth.
The dilemma he faces is what happens if Iraq's political leaders remain deadlocked for months on who should form a new government and spoilers try to take advantage of any power vacuum, as al Qaeda did after the 2005 election, sparking a wave of sectarian bloodletting.
"The concern is that that period is potentially perilous," said a senior administration official, speaking on condition of anonymity. "If there is any sense of a vacuum, who is in charge, one is always worried about how that vacuum is filled.
But, the administration is heartened by the fact that "as messy as things are, Iraqis, at least for now, have made a fundamental choice to resolve their differences through the political process, not bombs and bullets," he said.
The top U.S. commander in Iraq, Gen. Ray Odierno, says he has made contingency plans to slow the withdrawal of troops from Iraq, but Defense Secretary Robert Gates stressed there would have to be a "considerable deterioration" of the security situation first.
"It would have to be a cataclysmic scenario of the sort that most Iraq watchers don't think will occur, which means something of the sort of a return to the violence we saw in 2006," said Brian Katulis, an Iraq expert at the Center for American Progress think-tank.
Odierno says he still expects to reduce U.S. troop levels in Iraq to 50,000 by the end of August, from about 96,000 now.
There is little appetite in the Democratic-controlled U.S. Congress for delaying the pullout, particularly in an election year in which Democrats face a tough battle to hold on to their majorities in the Senate and House of Representatives.
"I find no support among my colleagues for anything other than continuing apace with the withdrawal," said Democratic congressman William Delahunt, a senior member of the House of Representatives Foreign Affairs Committee.
"We've been there, and it's time for the Iraqi people to make their own decisions," he told Reuters in an interview.
Washington would like to see a new government formed as quickly as possible, but officials acknowledge that it may be weeks if not months before a new parliament is seated, a prime minister chosen and his cabinet approved.
The U.S. official said Washington had no favorites in the race, but Katulis said victory by the Iraqi National Alliance, a mainly Shi'ite alliance that includes parties with links to Iran, would pose a problem for the United States.
Washington wants a stable, friendly government in place as it withdraws its remaining troops by the end of 2011, one that can also finally make headway on potentially explosive issues such as the future of the disputed oil-rich city of Kirkuk.
There is also speculation that Washington and Baghdad may revisit the security agreements they signed in 2008 to keep on a number of U.S. soldiers in Iraq after 2011 as trainers.
"When you are selling a country sophisticated hardware and deeply embedded with their military, it is more than likely that whoever comes into office ... is going to ask us to stay," said Brett McGurk, a former Bush administration official who helped negotiate a new U.S.-Iraqi security pact in 2008.
While Obama wants to wind up the Iraq war as quickly as possible, he doesn't want to leave the country in a mess.
After investing so much blood and treasure in Iraq, the United States -- even under a president who opposed the war when he was a U.S. senator -- wants to be able to hold up Iraq as a success story and say it was not all in vain.
That was underscored by Biden in an interview last month. "I am very optimistic about Iraq. I mean, this could be one of the great achievements of this administration," he said.
(Additional reporting by Susan Cornwell; Editing by Patricia Wilson and Eric Walsh)