In a sign of voter interest in the race, officials said the turnout even before Tuesday  through mail-in balloting  had surged. Of the state’s 64 counties, 46 were conducting elections entirely by mail under a law passed by the legislature last year intending to cut counties’ costs in running elections.

As of Monday, nearly 598,000 ballots had already arrived in the offices of county clerks and recorders around the state. That compares with about 488,000 votes cast in the entire 2008 primary, according to figures from the Colorado secretary of state.

This year’s high turnout was probably only partly due to the ease of voting from home, said Rich Coolidge, a spokesman for the secretary. “We also haven’t seen these kinds of contested primaries in some time,” he said.

The challenge for incumbents and establishment-backed candidates  to distance themselves from Washington  was clear in the tone of Mr. Bennet’s victory speech.

Though he was appointed to the Senate last year to fill a seat vacated by Ken Salazar, now Mr. Obama’s interior secretary, and had Mr. Obama’s support, Mr. Bennet said at Mile High Station in Denver, “I know one thing: Washington has a lot to learn from Colorado.”

He reached out to Mr. Romanoff’s supporters, saying that he would work hard to prove himself worthy of their support, but that in the end the things that divided Democrats were small compared with the issues that would be discussed in the coming midterm elections.