In the recent US presidential debate (where the Green and Libertarian candidates were excluded, even though they are on enough state ballots to win), Romney came out on top. This happened to surprise many, and I don't really know why. yes, Romney wasn't the best in many of the Republican debates, but he appeared to win a few of them. More crucially though, Obama, really, has no leg to stand on, anywhere. Nothing he has done has worked, Obamacare (and more crucially the personal mandate) is a disgrace, and this is basically all he has done. The economy is in tatters (Obama said he would not serve a second term if he didn't fix it, yet he still stands). Unemployment is excruciatingly high, and underemployment is still higher. U6 (the unemployment measure that includes these underemployed), is 14.7%, and did not move when the recent "increase in jobs" was announced. People are taking part-time, often short-term jobs when they really need full-time jobs. The economy is nowhere near fixed, and Americans know it - 14.7% are out of full-time work.
So it was quite possible that Obama would lose in the debates, that is fairly easy to understand, especially as he hasn't faced a debate opponent in this format since 2008, Romney has. What people are trying to figure out is why, after the debate, Obama's lead in the polls disappeared. It is unfathomable to many that such a lead would disappear so quickly. As has been rightly pointed out, such a large move, this close to the election, is unprecedented. I am not at all surprised. Why? Because something the political commentators keep mentioning but still overlook. Nobody likes either candidate. One is a proven failure, the other nobody likes. The main reasons that supporters seem to have is that their candidate is not the other guy. A major part of this election revolves around Big Bird, showing just how close the two candidates are on actual policy. The reason the polls shifted so quickly was that, both candidates have a large amount of soft support. Whilst they might have a solid base of say 20%, most of the US electorate would like a different set of choices. One of my US friends (a registered Democrat), hates Obama and the personal mandate that is his only real success. Yet, despite this, he still finds Obama preferable to Romney. Nobody likes either candidate, people are ready to jump to another candidate very quickly - and this is why the polls have shifted so much.
This is why, getting Gary Johnson and the Green candidate into the next presidential debate is still important. If a 10% swing can occur in one debate, it can happen in the next, and with a real alternative, it might make a big difference. This is quite possibly what the establishment are so scared of - a real alternative might prove to be hugely popular if given the chance.
The same is true of the UK - most polling companies still include UKIP in the "other" category, often unprompted on phone polls, yet they are currently above the Lib Dems in many of these, or at least in the same region. It is about time that both American and British politics was opened up a bit.