No surprise.

Although no final decision has been made because of family considerations, ABC News has learned that White House officials are preparing for Chief of Staff Rahm Emanuel to announce on Friday — as Congress adjourns for recess — that he is leaving his post to explore a run for mayor of Chicago.

White House officials expect that President Obama will also name an interim chief of staff, perhaps senior adviser Pete Rouse, at the announcement.

Sources close to Emanuel cautioned that he has yet to pull that last trigger on the decision…

Vice President Biden’s chief of staff Ron Klain, Deputy National Security Advisor Tom Donilon and White House deputy chief of staff Jim Messina are all said to be on the list of candidates from within the president’s inner circle and already working at 1600 Pennsylvania Avenue.

It was just this morning that The One was telling NBC that Rahm would have to move quickly if he wanted to take a serious shot at Chitown. Given how close we are to the election and how sore liberals are at him these days, I wonder if O will look to bring in someone with lefty cred to appease them. ABC floats David Plouffe as a possibility. Won’t he be too busy running Obama’s perpetual presidential campaign to run the White House day to day? And won’t his obvious interest in repositioning O a bit further to the center policy-wise ahead of 2012 mean he’ll be a total bust with the liberals his appointment would be designed to placate?

As for Rahm, I look forward to the cascade of nutroots blog posts tomorrow about how he ruined their dream of a great liberal realignment by being too centrist-y or whatever. Exit question: Are we confident that he’s going to win this mayoral race? He has every advantage, but remember — when it comes to this White House and Chicago, there are no sure things…