President Obama's hard-nosed chief of staff is expected to step down, possibly this week, to begin his pursuit of Chicago's mayoral office, according to reports citing people close to him.

"Rahm is nearing a decision on whether to leave the White House and explore a run for Mayor of Chicago — an announcement could come as early as Friday," an unnamed individual close to Emanuel told Politico's Glenn Thrush. "Because of family considerations, no final decision has been made."

Congress is expected to adjourn for recess on Friday.

"Ever since Richard M. Daley announced earlier this month that he'd step down as mayor next year after 22 years on the job, the question has been when -- and not if -- Emanuel would make his move," Salon news editor Steve Kornacki summarized. "The initial expectation was that Emanuel would stay at the White House through the midterm elections, the customary jumping off point for top aides looking to leave a White House. But the mayoral field is quickly taking shape in Chicago, and in the last few days, pressure had been growing on Emanuel to make his intentions clear. Emanuel apparently got the message."

As an Illinois congressman and chairman of the Democratic Congressional Campaign Committee, Emanuel engineered the party's takeover of Congress in 2006 and rose to a position in House leadership. Also a former aide to President Clinton, Emanuel was a key player in passing the North American Free Trade Agreement.

It had been speculated that he would stay at the president's side throughout the mid-term elections, but a filing deadline for Chicago mayoral candidates falls on November 22. If Rahm does indeed leave the White House this week, that will largely be seen as his driving motivation.

"Should Emanuel leave the White House, Obama is expected to choose an interim chief of staff," Real Clear Politics noted. "That's likely to be Peter Rouse, one of Obama's senior advisers in the White House and his former chief of staff in the Senate."

Emanuel first expressed his interest to run for Chicago's highest office during an interview in April. President Obama has previously said he would make an "excellent" mayor.