Barack Obama volunteer Marilynn Wadden rang more than a dozen doorbells in her first hour canvassing a tidy neighborhood here before stopping to take stock of her progress. Only a handful of voters were home, and, of them, only one agreed to have a ballot mailed to him so he can vote early. Two people said they supported the president but preferred to vote on Election Day. And another said he would back Mitt Romney.
"I wouldn't do this for pay. It'd be too discouraging," Wadden, a 70-year-old retired principal, said. She added that she works to re-elect the president "because in my heart I know how important this is."
If the race is close here and elsewhere, the outcome may come down to how well Obama volunteers like Wadden do their jobs - compelling everyone they can to go to the polls, especially those who are leaning Obama's way, but not a sure thing.
National and state polls taken before the first debate show Obama with a comfortable lead over Romney among Americans who are registered to vote. But the surveys also show Obama is locked in a tight race with the Republican among likely voters, a disparity that underscores the importance that turnout efforts will play in determining who wins the White House.
The latest Associated Press-GfK poll, for instance, found Obama with a commanding lead, favored by 52 percent of Americans to just 37 percent for Romney. Yet among those most likely to vote, the race was statistically tied, with Obama supported by 47 percent of likely voters and Romney by 46 percent. In Florida, a recent Washington Post poll showed the president ahead by 9 percentage points among all registered voters but up by just 4 percentage points among likely voters.
Such gaps suggest that the president has a significant opportunity - if not the need - to expand his vote if his enormous volunteer corps can persuade registered voters who are leaning toward him but don't always make it to the polls to turn out en masse on Election Day. It also suggests that Republican-led efforts to enact state laws restricting early voting periods and requiring voters to produce IDs - critics contend that disenfranchises minorities who tend to vote Democratic - could be important in denying Obama a second term.
Enter Obama's get-out-the-vote operation.
"Everything could come down to just a few votes," says Joan Tozier, a 62-year-old retired teacher who spends weekends in Obama's Sioux City office and every day making calls to neighbors from home. "I'm cautiously optimistic."
Four years ago, the Democrat's campaign identified new voters, registered them to vote, and then got them to polls on Election Day or during early voting periods. The effort was credited with helping put states that traditionally went to Republicans into the Democratic column, and helping Obama win the White House. Since then, Democrats acknowledge that enthusiasm has waned some among those foot soldiers.
Still, even Republicans acknowledge that Obama has an advantage on the ground in most if not all of the most hotly contested battleground states. In Iowa alone, Obama has 67 offices to Romney's 13.
Romney campaign political director Rich Beeson insists that the Republican nominee's ground-game efforts in Iowa and elsewhere are keeping up with Obama's.
"We have an equal number of contacts on the ground," Beeson said, adding that observers should "take into account the quality of the contacts, the number of contacts, not just the staff and offices."
Republican officials say they have more than four times as many phone calls to Iowa voters at this point than they had in 2008, and knocked on 16 times more doors in Iowa than at this point in 2008. Even before Wednesday's debate, they claimed more than 1 million voter contacts - by mail, phone and doorbell - so far this year in Iowa.
Romney's newfound momentum after his strong debate performance also helps him nationally. Republican officials say they have seen floods of new visitors to offices, with the RNC-Romney headquarters in Orlando, Fla., giving out twice as many yard signs as any other day and volunteers waiting outside to get in to make phone calls. In Nevada, new faces were waiting to volunteer when aides unlocked the doors at 8 a.m. And staff in Virginia made a push for supporters to recruit new volunteers to capitalize on the new buzz.
Republican officials say they will make contact with 5 million voters this week alone - the largest one-week total this year so far. A large share of that will come from the 2 million phone calls they plan on Saturday. Many of those calls will come from volunteers in Washington and Maryland who deploy for up-for-grab states Ohio, Virginia and North Carolina.
Republicans expect that their tallies at the end of the weekend will show volunteers have knocked on 6 million doors this year and spoken to more than 35 million voters.
Obama backers refuse to cede ground in their quest to turn out every voter they can.
Not registered to vote? Obama's team can help. Registered but not sure about plans on Election Day? Obama's campaign can mail you a ballot. Forget to return the ballot? Obama's volunteers offer a reminder. Need a ride to the polls? Obama's volunteers can drive.
Obama's volunteers appear to be having impact. Democrats report an almost 4-to-1 advantage among voters asking for ballots by mail in Iowa.
The vigor among the ranks appears to grow as Election Day nears.
"It's our time to go out and lace up our sneakers, put on our walking shoes," Norma Comstock, 71, a leader in the campaign's Sioux City office, said recently as she gave her fellow volunteers a pep talk. "This isn't a sure thing. We've got to fight every day between now and Nov. 6 so President Obama can keep fighting for us."
The other volunteers nodded and applauded.
Later, Comstock confided that she was worried about the president's re-election prospects, saying: "I'm really nervous. I was not last time."
Not that nerves are keeping volunteers from working hard; just the opposite, in fact. They're leaving nothing to chance, even going so far as to search for Democratic voters in this conservative swath.
Heidi Guggisberg-Coners, a Council Bluffs resident who is running as a Democrat for the Iowa House, has knocked on 7,000 doors in her district since June partly because of worries about Obama's turnout. "He will win some voters here, sure," she said. "But I wouldn't want this to be his firewall."
Volunteers also aren't resting on the notion that Obama will win; they brush aside polls that show Obama building a lead over Romney in this state.
"I don't think anything is a foregone conclusion," says Jill Slaughter, a nurse who spends her weekends knocking on doors for Obama and another night or two a week making calls. "You work until you can't do anything more."