Analysis: Obama won with a better ground game

(CNN) - Two days before Election Day, Vice President Joe Biden paid a visit to foot soldiers serving on the front lines of the 2012 campaign: suburban Colorado. Early voting had been under way in the Western battleground for weeks; the Obama team was counting on a volunteer army to deliver the state.

The polls in the race's final weeks had careened back and forth between razor-thin Obama and Romney leads. But Biden told the volunteers he wasn't worried - and they were the reason: "The ground operation which you guys represent is the best in the history of presidential politics."