Actually, Sarah was Obama's only opponent.
Well she did her level best to drag McCain kicking and screaming into the Presidency, doggonit!
The only real difference between McCain and Obama was on foreign policy.
That underlines the peril of Republican politics being defined more by what happens in the Middle East than by what happens here in the USA: it paves the way for someone like Giuliani to get close to the nomination, and for someone like McCain to wind up with it.
And thus the disaster of the election that just happened.