The current senator from Colorado, Michael Bennet, did something he's never done before tonight: he won an election. He won by a good eight percentage points or so.
Good analysis is victory agnostic, so here are truths that would also have been true even if Andrew Romanoff had won:
(a) Democratic turnout was high (though a bit lower than Republican turnout) and a lot of voters waited until the last minute to decide. That suggests that allegiances and branding are ephemeral and voters are skeptical of slogans and campaign tactics.
(b) Romanoff is a career politician; Bennet was a career corporate strategist and education innovator; the insurgent had more of a base than the incumbent, who had barely been in office; the incumbent was more deeply connected to the status quo than the guy who had been a politician for most of his adult life.
(c) It is very hard to determine whether Barack Obama significantly helped Michael Bennet, or whether Democrats saw in his endorsement of Bennet the opportunity to send a message of disapproval to Democrats in Washington by voting for Romanoff. Plenty of Democrats knew Obama's choice and chose someone else -- someone who wasn't previously a Republican (like Arlen Specter) and who WAS fully embraced by the White House political machine.