Iran's unpredictability in the region also has foreign leaders on edge. Any sign of aggression, particularly against U.S. ally Israel, would make an already delicate situation even more so.
Nuclear-armed North Korea is another constant source of concern.
Who would have guessed that Libya would turn into such a fall flashpoint?
But the Sept. 11 killing of four Americans, including U.S. Ambassador Chris Stevens, served as a stark reminder that the long fight against terrorism is far from over.
Late in the 2004 race, Osama bin Laden released a video threatening more attacks on the United States. It caused some clenching by the electorate, with many late-breaking voters deciding to stick with Republican President George W. Bush and a terror policy they knew. Democratic nominee John Kerry later conceded the video altered the dynamics of the final week of the race.
GUILT BY ASSOCIATION
As much as Obama and Romney mind their own camps, they're also at the mercy of others, to a degree.
Consider the dustup over Republican Indiana Senate candidate Richard Mourdock's remarks on rape and abortion. It put Romney on the spot because he had endorsed Mourdock and cut an ad for him, giving Democrats a new opening to criticize Romney and his party on women's issues.
Obama has been weighed down at times by his former spiritual adviser's charged rhetoric. Republicans also have tried to tar the president by highlighting companies that went bankrupt after receiving millions in federal stimulus money.
Forecasters were watching a powerful storm headed toward Florida and the East Coast that could bring heavy rain, snow and flooding to several states.
The Obama administration's response would be heavily scrutinized and candidate travel to Florida and other states could be disrupted.
The race already has been affected by one storm: the Republican National Convention in August was shortened by a day as a tropical storm bore down on Florida, Mississippi and Alabama.
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