Back in 2011, amid the discussions of withdrawal from Iraq, and the debate over how many troops would be needed to maintain a stable environment, two influential names rose to the surface, Tom Donilon and Denis McDonough. Both Donilon and McDonough overrode the Pentagon advice, and advised President Obama to dismiss the military and heed their counsel instead.
In August [2011], after debates between the Pentagon, the State Department and the White House, the Americans settled on the 3,000 to 5,000 number, which was reported in August. According to two people briefed on the matter, one inside the administration and one outside, the arguments of two White House officials, Thomas E. Donilon, the national security adviser, and his deputy, Denis McDonough, prevailed over those of the military.
Intelligence assessments that Iraq was not at great risk of slipping into chaos in the absence of American forces were a factor in the decision, an American official said. (link)






