At an Air Force Academy football game in Colorado Springs, Rep. Cory Gardner (R) campaigns for a hotly contested Senate seat. He’s running against Sen. Mark Udall (D), who doesn’t fare well in this deeply conservative pocket of the state. (Jeff Simon/The Washington Post)

Cory Gardner figures that what he needs to know about big-league politics he learned as a fullback and middle linebacker for an eastern Colorado high school so small that the guys had to play both offense and defense.

“I used to play against a high school football team that always used to run the single wing. And eventually, other teams figured out that they ran the single wing. And so they prepared for it,” the two-term Republican congressman said as he made his way through a game-day crowd at the Air Force Academy’s Falcon Stadium this month. “The Democrats are stuck running the single wing.”

In Colorado, the Democratic formation has been working pretty well.

Barack Obama carried the state in two runs for the White House. Republicans have not won a top-of-the-ticket race there in a decade. And Michael Bennet’s Senate victory in 2010 has come to be regarded as the prototype for how a Democrat can win in a tough year nationally. Bennet now heads his party’s campaign arm, the Democratic Senatorial Campaign Committee.

This year, Sen. Mark Udall (D), 64, is following that strategy again as he seeks a second term. It consists of convincing voters that Gardner, 40, is too far to the right, and then building a superior ground operation — in Udall’s case, one that Democrats say is three times as big as Bennet’s four years ago.

Sen. Mark Udall (D) says his opponent, conservative Rep. Cory Gardner (R), wants to do away with many women's rights and says Gardner is trying to "disguise" his positions and “distract” voters. (Jeff Simon/The Washington Post)

“If it works,” Bennet said, “we’ll win.”

The real question is whether it will work against a candidate like Gardner and in a year like this one. President Obama has become unpopular here; when he came to the state in July to raise money for Udall, the senator found a reason at the last minute to remain in Washington.

Colorado’s Senate race is one of the closest in the country and is widely viewed as a test of whether this state has completed its transition into the Democrats’ column. The contest for governor, between incumbent Democrat John Hickenlooper and former GOP congressman Bob Beauprez, also has tightened more than many had expected.

Adding to the uncertainty is the fact that, for the first time, every Coloradan will receive a mail-in ballot and can register to vote right up to Election Day. That is expected to help the Democrats — although by how much no one knows, given that Republicans are normally more inclined to vote in off-year elections.

“This election determines whether Colorado is blue or purple. It certainly won’t be red,” said former Denver mayor Wellington Webb, the first African American in that post.

Webb, a Democrat who served three terms, was at the opening of a Udall field office early this month in the historically black community of Montbello. He was wearing a “Ready for Hillary” pin on his lapel, along with one for Udall.

“If we carry the governor’s and senator’s races, we are going to be in good shape” for the presidential contest of 2016, Webb said.

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But what label do you put on the political philosophy of a state that one year would legalize marijuana for recreational use and the next year recall two state senators who voted for stricter gun laws?

“We’re a libertarian state — small ‘l’ — when it comes to privacy issues, issues of reproductive freedom, gun ownership, who you worship, who you spend your life with,” Udall said. “We’re a pro-environment state. We self-identify with environmentalists more than any other state in the nation. But we’re also very pro-business.”

Gardner said it is just as hard to pigeonhole Colorado’s taste in politicians: “We’re a state that sent [to the Senate] Tim Wirth, one of the leading left voices, and Bill Armstrong, one of the leading right voices. It’s a state that sent Ben Nighthorse Campbell to the U.S. Congress as a Democrat with overwhelming support. It’s a state that sent Ben Nighthorse Campbell to the Senate as a Republican with overwhelming support.”

Udall had appeared to be cruising to an easy reelection until Gardner surprised many here by giving up his safe congressional seat and jumping into the race eight months ago. The party quickly cleared the field for him.

Gardner argues that, as his ads put it, he is a “new kind of Republican.”

Stylistically, that is undoubtedly true. Gardner’s personality is sunny, and he is not prone to the kind of off-putting comments that got the Republicans’ last nominee, Ken Buck, in trouble. Buck compared homosexuality to alcoholism and once told a conservative audience that they should vote for him “because I do not wear high heels.”

Gardner is so relentlessly affable that his megawatt smile has become a talking point among Democrats. “A big smile’s a nice thing. I think we all have big smiles, but your record matters, your actions matter,” Udall told MSNBC.

In Gardner’s case, that record is solidly — and, Democrats say, extremely — conservative.

Where they have hammered him hardest is on social issues — particularly his past support for two Colorado “personhood” ballot measures, which declared that rights begin at conception.

Gardner says he has changed his mind on the issue, after he became convinced that the measures would have outlawed some forms of birth control. And in a jujitsu move that several Republican candidates are making this election season, he advocates making some forms of prescription contraception available over the counter.

As Gardner worked the crowd at the Air Force-Navy football game, one man he met joked, “You got any birth control pills on you?”

However, Gardner has continued to support a federal “personhood” bill and has deflected questions about the apparent inconsistency.

All this matters because of the women’s vote. In 2010, Bennet won in part because of what the exit polls showed to be a 16-point gender gap, one of the largest of any race in the country. Democratic strategists say privately that Udall must do nearly as well.

“This is the playbook that they ran in 2010, and it worked. They did it again in 2012,” Gardner said. “It’s a tired, old playbook. And as a result of the failures of the policies of this administration, it’s not going to work again, because people can see right through it.”

Winnetta Mahaffey, a retired Lakewood woman who supports Gardner, said,“Hopefully, the women will get a brain and realize the economy and jobs and immigration are top priorities, not abortion.”

The Denver Post — which endorsed Udall in his 2008 run, Bennet in 2010 and Obama twice — gave its nod this year to Gardner.

What the Post had to say about the candidate it did not endorse was brutal. In its editorial, the newspaper scorched Udall as having run an “obnoxious one-issue campaign” and wrote that he is “not perceived as a leader in Washington and, with rare exceptions such as wind energy and intelligence gathering, he is not at the center of the issues that count — as his Democratic colleague, Sen. Michael Bennet, always seems to be.

Asked in an interview prior to the Post editorial whether he risks being a one-note candidate, Udall argued that reproductive issues speak to a broad swath of women’s concerns.

“This is about fundamental freedoms. It’s about economic opportunity. It’s not a social issue,” Udall said. “The irony is that my opponent has been a social-issues warrior, and the reason this keeps coming up is that he’s built his entire political career on attempting to limit women’s access to reproductive health services.”

“He’s on the wrong side of the freedom and opportunity and respect debate,” Udall said.

Udall has a sports metaphor of his own to sum up where things stand as the race heads into its final weeks. In August, he achieved a personal goal of climbing the last of Colorado’s 100 tallest mountains. As he and his wife, Maggie Fox, were rappelling down the more-than-13,000-foot Dallas Peak, two other climbers recognized him and yelled: “You have our vote!”

He got there, Udall tells supporters, the same way he wins elections.

“You don’t schmooze your way up a mountain. You don’t trash-talk your way up a mountain,” he said. “You just climb the doggone thing.”

Alice Crites contributed to this report.