I think it’s simple. Obuma showed himself as a sneering, 50 IQ Marxist with dead, black eyes and no soul or heart.
That he is, but many people couldn't plainly see it, until they had someone else to compare him to, side by side. That finally happened in the first debate, and Romney took the lead from that point, forward.
Considering sociopaths are merely chameleons, all he could do in the last debate was pretend. Unfortunate for Obama, he was supposed to be more assertive, not stare like a lunatic (which is something I am certain women noticed).
The fact that Romney wasn't fazed in the slightest and spoke confidently to his face, with command of the issues, showed Obama to be a giant phony to all who were disinterested enough to only realize it now, but had not yet drunk the Kool-Aid.
Consequently, Obama was rendered powerless and his poll numbers show it.