Colorado was one of three states holding primary contests on Tuesday, February 7, 2012, the other two being Missouri and Minnesota. Colorado's results were the last to come in.
Mitt Romney was expected to do well in Colorado, because he had done well there in the 2008 primary contests, and because some of the demographics there, such as Mormon voters and educated, affluent voters. In Colorado, as in the other two states voting, the campaigning was rather sedate, with none of the expensive advertising that marked Florida.
As in the other two states, Rick Santorum, previously an "also-ran" had a very good night. Although he did lose Denver and its suburbs to Mitt Romney, he managed to do quite well in other parts of the state, winning the state with 40% of the vote to Romney's 35%, Newt Gingrich and Ron Paul coming in a distant third and fourth with 13% and 12%, respectively. Santorum's win in Colorado was perhaps even more of a surprise than it was in Missouri or Minnesota.
The reason that Romney did so poorly, even in a state that is considered one of his bases, is being debated widely at the moment. Colorado, like Minnesota, is a caucus state, and therefore attracts more conservative voters. It could also be that Romney needs considerable television advertising, like he had in Florida, to do well. Or it could be a reaction against Romney's position as the "inevitable" nominee. In any case, along with the other two contests, Colorado has reopened the race. It also means that Santorum has now won four states, more than any other candidate, and has also won in different regions of the country.
The primary contests of the night were supposed to be rather sedate and unimportant, but with Santorum's sweep, they have been one of the most dramatic results of the campaign.