A concise article by Thomas Sowell at RealClearPolitics. Please link through and read, as it will take less than two minutes. Here's the general idea:
The point when it is safe to begin pulling out is the point when the Iraqi military and police forces are strong enough to continue the fight against the terrorists on their own.Sowell cites a Brookings Institute report, authored by Michael E. O'Hanlon and Kenneth M. Pollack, which states that the surge is actually working. Surprise, surprise. What is most surprising, though, is the MSM's deafening silence about any positive events or progress being made in the war in Iraq.
That point depends on how much and how long the current progress continues, not on how much the Democrats or their media allies need an American defeat before the 2008 election.