That may not happen even if Obama is president:

Iraq is a sovereign country. Not just according to me, but according to George Bush and John McCain. So ultimately our presence there is at their invitation, and their policy decisions have to be taken into account. I also think that Maliki recognizes that they’re going to need our help for some time to come, as our commanders insist, but that the help is of the sort that is consistent with the kind of phased withdrawal that I have promoted. We’re going to have to provide them with logistical support, intelligence support. We’re going to have to have a very capable counterterrorism strike force. We’re going to have to continue to train their Army and police to make them more effective.
You’ve been talking about those limited missions for a long time. Having gone there and talked to both diplomatic and military folks, do you have a clearer idea of how big a force you’d need to leave behind to fulfill all those functions?
I do think that’s entirely conditions-based. It’s hard to anticipate where we may be six months from now, or a year from now, or a year and a half from now.

I’m glad he’s changed his position on this but I don’t know if we can trust him. Who knows what he’ll do until he becomes president. He’s still saying that he’ll end this war. Maybe in his mind the support he’s intending he doesn’t consider “war” maybe he’s thinking support and not “war.” So, if he leaves troops there he can say that they are for “security” purposes not because we are technically fighting a war.