What McCain Has Going For Him
John McCain is helped by men and Mormons in Colorado, as well as the social/religious conservative base who love and are energized by Sarah Palin even if ambivalent about him. Republicans have long outnumbered Democrats in this part of the world, with most of the independent, libertarian, and/or former Perot voters typically leaning Republican over the Democratic candidate when given only two viable choices. Indeed, only LBJ in 1964 and Clinton (due to the Perot-voting split of the conservative vote) in 1992 have taken Colorado for Democrats since Truman. It's a state whose independents would have bought McCain's maverick argument in 2000, and indeed McCain's fundraising is in the top 25% of states. McCain has made trips to the Western Slope, where he needs to rack up a big margin in Grand Junction (Mesa County) if he is to have any hope of holding down the losses in Denver.
What Obama Has Going For Him
Demographically, factors that favor the Democrat include many young voters and, in this race, very few elderly voters favors Obama. Starbucks overwhelm Walmarts, and despite hosting the epicenter of religious Republican conservative politics in Colorado Springs, only 15 states have a higher percentage of same-sex households. Colorado is also a highly educated state, and despite being a Mountain West state, has a lower than the median gun ownership rate. Colorado has an increasing number of Latino voters, and only nine states donated money to Barack Obama at a higher per capita rate. Finally, Barack Obama appears to have gotten a huge benefit from the Democratic National Convention taking place in Denver, as thousands of new volunteers around the state traded volunteer hours for tickets.
What To Watch For
Marilyn Musgrave, the Republican House incumbent representing the eastern third of the state, is in a very tough re-election fight against Democrat Betsy Markey. Few House members this side of Michele Bachmann would Democrats like to see go down more, given her public antipathy for Americans who are gay. In the presidential race, if Obama reaches 40% in a place like Mesa County (Grand Junction) or in El Paso County (Colorado Springs), then goodnight sweet prince. To have any prayer, McCain needs to hold Obama way down at the low 30% area (Gore and Kerry levels) in those places and hope that voting problems in Denver hold up the vote there. John Elway stumped for John McCain, but even his late-minute heroics likely won't be enough.
If you're John McCain and one of the things that is counted as a positive for your campaign is a small religious minority (Mormons) that makes up just over 2% of the entire population of the state then you're in bad spot.
I think Sean's analysis of the margins that McCain must hold Obama to in Mesa and El Paso counties is spot on. In Denver Obama needs to hit 70%+. In 2006 Ritter won Denver with 77.6% of the vote on his way to a landslide state wide victory. In 2004 Kerry won Denver with just under 70% and lost the state by some 5 points, Ken Salazar won Denver with 73%. Salazar captured the election by 100,000 votes, he won Denver by 110,00. In 2000 Gore captured just 62% of the vote in Denver (Nader was well over 5%) and lost the state by 8 points.
Turnout is the other variable here, high turnout in Denver is critical for state wide Democratic victories. In 2000 Denver turned out just under 200,000 voters, in 2004 that number surged to nearly 239,000 voters. There are about 410,000 registered voters in Denver county and 48% of those voters are Democrats. Turn out in the neighborhood of 60% would be 240,000 voters - roughly equivalent to the turnout in 2004. I think you can expect significantly higher turnout than that and I believe that Obama will enjoy support of at least 75% of those voters.
The swing counties of Arapahoe and Jefferson will of course be important as well but I think high turnout in Denver will help Obama offset close races in Arapahoe and Jefferson. Kerry lost those counties by 4 to 5% in 2004, Ritter won them by nearly 20% in 2006. Obama doesn't need to match Ritter's margin though. If Obama can come close to or match Salazar's 2004 performance (+7 in Arapahoe, +3 in Jefferson) Denver will be able to pull him over the line. If Arapahoe and Jefferson go big (10%+) for Obama then the Presidential election is a blowout.