Israel and Iran
Foreign policy differences are unlikely to determine who wins in November. The economy is the most important issue to voters, and after that, other things like energy, immigration and social issues typically rank higher than foreign affairs. But Obama and even Romney would be thrown into a different race if Israel strikes Iran, as some foreign policy analysts fear will happen, and even Defense Secretary Leon Panetta warned is possible.
In that scenario, Obama is the most vulnerable — his every reaction and response will be calculated and scrutinized, and probably critiqued by Romney. If oil prices rise, Obama will be on the defensive on the home front, too, in addition to deciding whether to send U.S. troops to defend Israel.
The best-case scenario for Obama is that he shows deft leadership, makes the calls that prove to be right and gets the country to rally around him. The worst case for him is that he stumbles or looks weak, effectively stripping away the foreign policy chops he earned by authorizing the raid that killed Osama bin Laden. Regardless, Romney's role is much less impactful, as he'd be simply reacting to the cues from the White House and standing to benefit from any missteps.
"President Obama's response would be very important at that point," Judy said. "It would be much more about Obama."
Terrorism or Natural Disasters
The most unpredictable of events could be the most unlikely, but also the most dangerous for Obama politically.
The 9/11 attacks initially caused Americans to stand behind Bush, bringing about a sense of unity. If another attack were to happen before the election, while some Republican critics might argue that Obama didn't protect the country, it's more likely that people will come together as they did in 2001, strategists say.
"There's also the rally-around-the-president effect," Fleischer said.
A natural disaster, though, could be more delicate. "It's the response to things like that that make or break careers," Judy said.
The memory of Katrina, and Bush's struggling response to it, is still fresh in many Americans' minds. Bush's second term was marred by the devastating storm, though some governors in affected states who responded swiftly were rewarded with positive approval ratings.
Obama hasn't bungled any responses to natural disasters, including the BP oil spill, Hurricane Irene, and tornadoes and flooding in the South.