Over the fiscal cliff: What kind of landing?

Efforts to save the nation from going over a year-end "fiscal cliff" were in disarray as lawmakers fled the Capitol for their Christmas break. "God only knows" how a deal can be reached now, House Speaker John Boehner declared.

President Barack Obama, on his way out of town himself, insisted a bargain could still be struck before Dec. 31. "Call me a hopeless optimist," he said.

A look at why it's so hard for Republicans and Democrats to compromise on urgent matters of taxes and spending, and what happens if they fail to meet their deadline: