The first brigade could not arrive until January of 2010 and after that the need to build facilities to house more troops would limit him to just one additional brigade every three months. If the president were to grant McChrystal's full request of 40,000 troops it would be 2011 before they all got there.
That's bad news for the war since McChrystal has warned it could be lost in the next 12 months, but it also means the president has plenty of time to decide whether to give McChrystal all the troops he wants.
The White House is not happy with the way senior military leaders, beginning with Joint Chiefs Chairman Mullen, have handled the debate over Afghan strategy - boxing the president in with their public statements. Two days after the president held his first meeting on Afghanistan, Mullen was telling Congress he agreed with McChrystal.
"Having heard his views and having great confidence in his leadership, a properly resourced counterinsurgency probably means more forces," Mullen said.
CBSNews.com Special Report: Afghanistan
Even before that General Petraeus, the overall commander for the region, gave an interview in which he strongly backed McChrystal's assessment.
As for McChrystal, he publicly dismissed a much more limited strategy favored by Vice President Biden.
"A strategy that does not leave Afghanistan in a stable position is probably a short sighted strategy," McChrystal said.
The Afghan decision is the president's first moment of truth as commander in chief. It is also shaping up as a watershed in his relations with senior military leaders.