By all accounts, the 2012 US Presidential election should be locked up by President Obama at this point. Most reliable, statistically based models give his re-election chances between 65 and 75% after the two conventions, even though the popular vote margin is only around 2-3%. Still those numbers are usually pretty good bets in a Presidential election.
However, there is one major variable in the mix that neither political party can control. The Republicans stand to benefit from an international policy debacle that the current President finds himself faced with. The international Islamic response to a low-budget film that mocks the Prophet Mohammed.
While the current protests against the film, some of which have turned violent, hasn't emerged into a full-blown crisis, it has the potential to do so. While the Arab Spring initially looked like an international policy coop for President Obama, the same ant-establishment energy that was turned against dictators now has the potential to be turned against the United States.
In other words, if the international Islamic community decides to turn blame for the movie on the US, rather than the individual who made it, and continues to pursue violence, this will create an atmosphere of fear in the United States. And Americans will increasingly question the President's international policy and perhaps decide that they'd like the harder line stance of Mr. Romney.
If Romney wins the election at this point, it will most likely be due to the average citizen's perception of a failed international policy emerging in Islamic wrath at US embassies around the world.