First Lady Michelle Obama fired up a capacity crowd Wednesday in a Colorado county whose voters could wield an outsized influence over who wins the presidency. Promising a close election, she urged supporters to approach every potential voter as the one who could help her husband, President Barack Obama, win a second term.

“Every call, I want you to think one more person. With every door you knock on, think this could be the one. With every conversation you have, this could be the one that makes the difference,” she told an enthusiastic crowd of some 2,800 campaign volunteers and others who filled the Arapahoe High School gymnasium in Centennial for the mid-day rally.

In a sign of the importance the presidential campaigns are assigning to Colorado’s nine electoral votes, Obama’s visit came just four weeks after her husband made a pair of stops in what most observers agree is one of a handful of crucial swing states. Presumptive Republican nominee Mitt Romney has visited Colorado twice in recent months following a flurry of campaign events in late January and early February surrounding Colorado’s caucuses.

Analysts say that the Colorado vote could be decided by voters in suburban Arapahoe County, along with voters in the state’s other bellwethers, Jefferson and Larimer counties. Recent polling shows Obama and Romney in a dead heat in the state.

“You know, this feels like four more years, right?” she asked the crowd as she took the stage.

Obama began with remarks directed at the firefighters battling forest fires in Colorado, including the massive High Park blaze, and those in their path. Saying that the first family’s “hearts and our prayers are with all of the families affected by the fires,” she added a “special thank-you to the brave firefighters and first responders.”

Then she turned her focus to the Obama administration’s record and sounded the dominant theme of her husband’s campaign.

“We can’t turn back now. We need to keep moving forward,” she said as the crowd cheered a slogan they had heard more than a few times from earlier speakers at the event. “That’s what we’re working for: truly, the chance to finish what we started,” she continued. “The chance to keep fighting for those values we believe in, that vision that we all share.”

Elaborating on a list of the administration’s achievements touted in a video that preceded her speech, Obama ticked off what the campaign hopes becomes a familiar litany: reversing the massive job loss that greeted Obama when he was sworn in, posting 27 straight months of private-sector job growth, passing a controversial health-care reform package, ending the Iraq war and killing Osama bin Laden.

She also highlighted the administration’s recent moves “to lift the shadow of deportation from many of these young people, who came here as children and were raised as Americans,” and praised the end of the “Don’t Ask, Don’t Tell” policy that barred gays from the military, drawing thunderous cheers. (The audience interrupted Obama’s roughly 30-minute speech more than 60 times with applause.)

“I could go on and on and on,” she said, and an audience member shouted out, “Please do!”

A smiling Obama demurred, noting that she didn’t want anyone passing out in the crowded, quite warm gymnasium.

Obama continued on to Pueblo that afternoon for a similar rally that drew roughly 1,000 people to the Creative Arts Center on the state fairgrounds. On the way there, along with her daughters Malia and Sasha, the first lady surprised lunch-time customers at Nacho’s Restaurant, where she posed for photos and shook hands.

The first lady is wildly popular, surpassing her husband and his opponent in favorability ratings, according to recent polling. According to a Gallup poll released a few weeks ago, 66 percent of Americans view Michelle Obama favorably, while at the same time an ABC News/Washington Post poll showed the president with 52 percent favorability and Mitt Romney at 41 percent.

Stacy Kupzyk, an Obama campaign volunteer from Parker, introduced the first lady at the Centennial event with a story about her 1-year-old son Max, who has surmounted severe health problems in recent months, and offered an endorsement of the Affordable Care Act, which she fondly dubbed “Obamacare.”

“Obamacare means that kids with preexisting condition can’t be denied coverage anymore,” she said. “Obamacare means that insurance companies can’t drop you just because you get sick. And it means that my son Max will be able to grow up healthy and work hard without having to worry about his health care.”

Blasting Romney for a recent suggestion that some of the health-care legislation’s foundations should be reversed, she told the crowd that the difference between the two presidential candidates was clear.

“We need everyone to understand how important this election is,” Kupzyk said. “And that a lot of progress we’ve made, like heath reform, hangs in the balance. We need to talk to our friends and neighbors about it and let them know our president has their back.”

Organizers worried they had given out too many tickets to the Centennial event — it looked like nearly everyone who picked up a ticket had shown up — as lines snaked around the approach to the school on Wednesday morning, but in the end everyone made it inside the gymnasium, packing the bleachers and crowding the floor.

Romney filled the same high school gymnasium — with a couple hundred more supporters packed into an adjacent overflow room that had been commandeered by the Secret Service for Obama’s visit — on the eve of Colorado’s Republican caucuses in early February. The next night, Romney ran second behind Rick Santorum in the nonbinding presidential poll that kicked off an arduous process to select delegates to this summer’s Republican National Convention.

Republicans took advantage of the first lady’s visit to the state to hammer Obama’s record on the economy and argue that he doesn’t deserve another term.

“President Obama’s campaign would like us to believe that everything is just fine,” said Colorado Republican Party Chairman Ryan Call in a statement to The Colorado Statesman, “but with over 220,000 Coloradans out of work, it’s clear Colorado’s families and small businesses have suffered under Obama’s failed leadership. Barack Obama simply hasn’t lived up to the promise of his 2008 campaign, and more empty rhetoric from his campaign cannot erase nearly four years of broken promises and policies that are hostile to the local businesses and job creators that drive our economy.”

But Aurora residents Lisa Napper, 17, and Rodi Wooten, 70, sporting ear-to-ear grins as they made their way outside after the rally, disagreed.

“People will see what President Obama has done and what he has given, and where he intends to go,” said Wooten. “One of the things Michelle stressed, that’s very prominent with the people around me, is his character and his values and his vision, and that’s what puts him way ahead of any possible candidate.”

She also expressed optimism about the economy.

“It is going forward, it’s inching forward. What would you expect with that kind of loss? For the years that he’s been in, he’s been remarkable, considering what he inherited. I think that’s so clear. People are acting like somehow magically we were supposed to be where we were before, and that’s impossible, considering what he began with.”

Napper, a senior this fall at Rangeview High School, said she trusts Obama to improve the economy and make it easier for her to consider college and her career without worrying so much about student-loan debt.

She’s been a fan of Obama since she had the chance to meet him five years ago, before he had announced his run for the presidency.

“My mom said, ‘This man is going to be the next president,’ and she had to drag me out of bed to go and I was so mad, and then we went and stood there for like three hours and I was like, ‘Who is this man? Why are we standing out here?’ Afterwards, we were coming outside and he was coming out to go to his car, and he didn’t have the Secret Service, because he was just a senator, and we got to talk to him and shake his hand, and from that moment I was like, ‘OK, he’s going to be the next president.’”

—Ernest@coloradostatesman.com