Another fight over the debt ceiling might be just around the bend, but a key member of the White House financial team won't be here to see it: Bloomberg reports that Treasury chief Timothy Geithner, who has long planned to leave his post, will do so at the end of this month. The leading candidate to replace him remains White House chief of staff Jack Lew, though he'd likely need a deputy with a strong Wall Street background. The White House reportedly reached out to American Express CEO Kenneth Chenault as a potential Geithner successor, but he is opting to stay in the private sector, according to Bloomberg's insiders. (More Timothy Geithner stories.)