John McCain has supported the Iraq war from the very start, and although he disagrees with Bush's recent actions, he believes we are winning and Iraq and is willing to send in more troops to solidify that "victory". He has barely changed his stance on the war since 2002, when he voted for it under President Bush. He disagrees with Obama's desire to withdraw some of the troops from Iraq.
He believes that leaving from Iraq sends al-Qaeda the message that we're giving up. It also means that we are giving up on creating a competent, trained and capabled Iraqi security force to keep peace in the region and to eventually create a working government. He thinks that we cannot withdraw troops right now because we haven't yet completed our supposed primary objective.