The world's leading futurologists have four theories.

Cascio clearly believes that humanity has the ingenuity and the smartsto beat back threats to its continued existence. He doesn't, however, assume that the persistence of the United States is necessarily the most-desirable outcome. It's possible America will collapse as we try desperately to save it—or perhaps the country will shrivel up and go away when its time has come and gone. "It's not necessarily how America will survive," Cascio says, "but how do the values we hold dear … survive even if some of the institutions don't?"

You've seen what the professional forecasters think. Now we want your thoughts on America's demise. With our "Choose Your Own Apocalypse" tool, you can pick the scenarios you think are most likely to terminate the United States and compare your selections with those made by the rest of the Slate audience. At the end of the week, I'll file a report on the most popular choices and investigate what clues your favorite scenarios give us about the American psyche.