What is the situation going into the election?
In '08, McCain beats Obama (betrayed by Hillary, who wants to be sure to be elected in 2012 but tumbles amid scandal in 2010).
McCain serves only one term. His presidency is a failure, due to weak economy, an abyssal fiscal deficit, a civil war in Pakistan and Israeli failed strikes in Iran that McCain does not succeed in preventing.
Dems are so desperate to have lost in 2008 that they want a real fresh face (Obama isn't anymore and is hated for having lost an unlosable contest, like Gore in 2000).
GOP is forced to nominate a woman after an old white man and still no Black.