The current situation is "semiseparation," says Mr. O'Hanlon. He estimates that about half of the possible ethnic cleansing that could occur in mixed neighborhoods, has.
Today Baghdad neighborhoods are separated by miles of security walls and blast barriers.
"If you get an [Iraqi] security force that is capable enough, get a couple of rounds of elections, more economic growth, there is a chance to take down those barriers," says O'Hanlon.
But it is only a chance, and a small one at that, he says. The worst-case scenario would be a return to the levels of violence of 2006 – times two. With such a resumption "at some point you would have complete ethnic cleansing," he says.
Iran ascends while US bogged down
Iran is one nation that seems poised to gain from Iraq's current situation. As Iraq's largest neighbor and a Shiite Muslim state, it has close ties with the current Shiite-dominated Iraqi government. Hussein and his Sunni-led regime, with whom Iran fought one of the bitterest regional wars of the late 20th century, is gone.
That does not mean Iran now wants Iraq to remain weak and unstable. To the contrary, Tehran has good reason to work for a stable and democratic Iraq, Iranian analysts say.
"In the next five years, Iraq should be united, with a Shiite government, without American troops, but with good relations with Iran and more secure," says Amir Mohebian, political editor of the conservative Resalat newspaper in Tehran.
At the moment, the US presence in Iraq is in Iran's interest, he says, to prevent radical Wahhabi Sunnis from helping Sunni insurgents form a Sunni state. But that does not mean Tehran needs to make things easy for US forces, he adds. Many US officials have accused Iran of passing lethal weaponry to an array of anti-US resistance groups.