Here is video of Barack Obama in January 2007 clearly saying that the "Surge Strategy" would make no difference on the ground in Iraq. In the video, that statement is juxtaposed against his Political guru - David Axelrod - saying in late May 2008 that Obama always knew an increase in troops in Iraq would lead to a reduction in violence there. That is now Obama's talking point on the subject, but it is clearly not true:

Obama on January 14, 2007:

"We can send 15,000 more troops, 20,000 more troops, 30,000 more troops: I don't know any expert on the region or any military officer that I've spoken to privately that believes that that is going to make a substantial difference on the situation on the ground."

Wake Up America blog has a very detailed article that includes this video, and a lot of other analysis on Obama's attempt to cover-up his previous opposition of the surge and what he said about it at the time.