While recent polls favor Obama, the presidential race is close enough that both camps are campaigning here into Election Day.

The biggest question: When will we know the results? According to The Denver Post today, the high volume of mail-in ballots may delay results until Wednesday.

Most county clerks in the big Front Range counties said they expect to go into Election Day “clean,” meaning the only votes left to count will be those cast Tuesday.

…. Arapahoe County Clerk Nancy Doty said of the multistep verification and counting process that mail-in ballots must undergo. “It’s a lot of work. So we’re not going to be done by 1 or 2 in the morning.”

More than half of Colorado’s three million registered voters used early voting or mailed in their ballots. Of those who requested mail-in ballots, 70 percent have already returned them. But 500,000 are expected to come in today and tomorrow.

Those numbers are why Secretary of State Mike Coffman draws a difference between the “front end” of Election Day, when people are voting, and the “back end,” when clerks count the votes. Coffman said the back end “will be tough.”

While the votes are being counted as they come in, no tallies are made until after the polls close. Here’s a graphic showing the party breakdown of mail-in ballots and early voting to date. While more Democrats than Republicans have voted so far, 36.8 percent of the early votes are by unaffiliated voters.

Via an email I received, the Colorado Democratic Party is holding an Election Night celebration party at the Sheraton Denver Hotel (formerly the Adams Mark). Doors open to the public after the polls close at 7pm. If Senator Obama sweeps the Eastern states like Florida, Ohio and Pennsylvania, we may have a winner early enough for the Dems’ celebration party. But if Senator McCain takes one or more of them, it could be a much longer night.