We’re reaching a McBama moment in Iraq when realities on the ground may force positions of the candidates to converge.

The McBama moment could favor Sen. Barack Obama over his rival, but only if he fully grasps the current situation in Iraq.

Last week, Iraqi Prime Minister Nouri al-Maliki and aides raised the issue of withdrawal of U.S. troops. Iraqi officials are negotiating a formula to legally define the status of American forces in Iraq, after a United Nations mandate expires at the end of 2008.

The Democratic candidate cited Maliki to support his call for a 16-month withdrawal timetable. He’d been under fire last week for “flip-flopping” by suggesting he’d “refine” his Iraq policies if elected, so Maliki’s remarks were sweet music.

That music, however, may be deceptive. Any candidate who wants dramatic drawdowns during his first term needs to pay close attention to complex shifts going on in Iraq and the Middle East.

This is a time of enormous flux in Iraq, as it is around the globe. A year ago, Iraq’s security situation was still dire. A few months ago, no one expected a floundering Maliki to become a nationalist hero. Any U.S. president will have to “refine” his Iraq positions in 2009.

But it is essential to understand what’s happening now.

Maliki and his aides have been waffling on the issue of a timetable. His national security adviser, Mowaffak al-Rubaie, talked of a “time line horizon.” Government spokesman Ali al-Dabbagh spoke of “three, four or five years.” Iraqi sources tell me that a spokesman for Grand Ayatollah Ali al-Sistani has denied that the preeminent cleric had endorsed a timetable.

What’s going on? First, intense Iraqi political jockeying in advance of provincial elections later this year. Second, intense pressure on Iraqi political factions from Iran (more about this below).

On the first point, Maliki’s political faction is small and weak, so he is playing the nationalist card. Improved security is triggering nationalist feelings among majority Shiites, who previously tolerated the Americans from fear of Sunni insurgents.

But, while displaying independence, Maliki is still hedging his bets. He knows the reason Sunni insurgents are no longer a problem is that 100,000 of them are now on the U.S. payroll. They still need to be integrated into the Iraqi political system.

He knows he was able to curb radical Shiite militias in Basra only when American forces came to his rescue. Iraqi troops weren’t yet able to do it on their own.

In other words, the security gains within Iraq are still a work in progress. Upcoming provincial elections will hopefully cement Sunni political participation. Increasing public trust in Iraqi security forces will, hopefully, create a real national army.

But the Iraqi body politic is still extremely fragmented. There is still violence and mistrust within and between sectarian groups. Four million refugees, both inside Iraq and in nearby countries, provide rich fodder for those who still want to destabilize the country.

These social and political fragments swirl around like pieces in a kaleidoscope, continually forming new patterns. The reason for the progress of the past year is that Gen. David Petraeus and Ambassador Ryan Crocker have repeatedly taken advantage of these shifting patterns. Examples: When Sunnis rose up against al-Qaida, or when Shiites tired of radical Shiite militias, Petraeus and Crocker backed them up.

Yet Iraq is still splintered. More time is needed to solidify the pattern before a definitive time line is set. My guess is that Maliki will settle for a vague withdrawal horizon. Some form of agreement on retention of U.S. troops for a couple of years will probably be reached.

A smart presidential candidate would recognize that surging nationalism will limit the length of a large U.S. troop presence. Iraq is not Japan or South Korea, where troops could remain for 50 years. He would also recognize most Iraqi leaders still aren’t ready for all U.S. troops to leave.

Another key reason for their hesitation is their reluctance to be dominated by Iran. Tehran has been pressing Maliki and other Shiite factions to reject a troop agreement. When I asked Iranian foreign minister Manouchehr Mottaki last week in New York what Iran’s reaction would be to such an agreement, he replied flatly: “It is our understanding that they (the Iraqi government) will not sign it.”

But Iraqi leaders, including Iran’s Shiite co-religionists, do not want to be controlled from Tehran any more than they want American domination. Nor do they want Iran and the United States to fight their battles on Iraqi soil.

Obama has recognized that Iran is central to Iraq’s stability and called for talks with Tehran without preconditions. He ought to recognize that a time line for withdrawal of U.S. troops is an essential card in such negotiations.

Setting a fixed time line now would leave Iraqis dependent on Tehran and undercut any U.S. leverage. It would make it harder to solidify the current gains. Maliki knows this; that’s why I doubt he’ll insist on a date certain. Nor should any president who hopes to withdraw most U.S. troops in his first term.