A terrorist attack on presidential candidates could throw the US into unprecedented political turmoil. So why do so few people want to talk about it? WORST-CASE SCENARIO number one: It's the night before Election Day. Across America, voters turn on their televisions hoping to catch the final hours of the presidential campaign and instead hear the awful news. In coordinated attacks, terrorists have killed their favored candidates for both president and vice president. Now what?The answer in both cases -- and several equally unpleasant variants: Nobody knows.