(CNN) -- Two days before Election Day, Vice President Joe Biden paid a visit to foot soldiers serving on the front lines of the 2012 campaign: suburban Colorado. Early voting had been under way in the Western battleground for weeks; the Obama team was counting on a volunteer army to deliver the state.
The polls in the race's final weeks had careened back and forth between razor-thin Obama and Romney leads. But Biden told the volunteers he wasn't worried -- and they were the reason: "The ground operation which you guys represent is the best in the history of presidential politics."
"I'm telling you, it's this way in Virginia, it's this way in Florida. ... And I think that the one thing that is going to fundamentally make the difference is you guys -- for real," Biden said. "I'm not just trying to be nice. I really genuinely believe that's the deal."
Republicans, surveying the very same landscape at the very same time, sounded a much more skeptical note.
"We are poised to blow the Obama campaign out on Election Day thanks to a superior GOTV (get out the vote) program," Republican National Committee political director Rick Wiley wrote in a memo sent the day after Biden's Colorado visit. "The Obama campaign's superior ground game is a myth," said Wiley, promising a GOP victory. "It's (ground) game over."
Just one day later, Republicans were echoing the vice president's assessment, with one top Republican telling CNN: "Their (ground game) deal was much more real than I expected."
On paper, Democrats' turnout efforts this year dwarfed those of their GOP counterparts. The 125 million voter contacts the Obama team claimed were more than twice the Republican total. The hundreds of Democratic field offices outnumbered GOP outposts by greater than 2-1 or 3-1 in key swing states.
But the Obama campaign insisted it wasn't just about the numbers.
"Many field campaigns have historically favored quantity over quality. We do not," Obama national field director Jeremy Bird told reporters just before Election Day. "These are not phone calls made from a call center. They are done at the local level by our neighborhood team leaders, members and volunteers, who are talking to people in their communities."
And in an election cycle where billions of dollars were spent on attack ads -- far more than ever before -- that kind of old-school retail politicking may have made the difference.
In the home stretch, the Romney campaign pointed to a big jump in voter contacts this year over John McCain's 2008 effort. But a significant percentage of the voter contacts they pointed to included indirect contact -- like door hangers -- that didn't give voters the all-important sense of personal connection.
Meanwhile, the Obama campaign's turnout effort flooded the zone. While Republicans were still battling for the nomination in the spring, the number of Obama field offices in key primary season states likely to play significant roles in the fall -- states like Ohio, New Hampshire and Florida -- already outnumbered those of all his potential GOP challengers combined, even though the president wasn't facing any primary season challengers.
Even with a massive infrastructure advantage and major head start, an Obama edge on the ground was no sure thing. Republican enthusiasm was far higher in 2012 than it had been four years earlier, and indications were that Democratic enthusiasm had slipped. Well-funded super PACs took on some ground game efforts for the Romney campaign, and polls conducted in the home stretch found voters in the most hotly contested battlegrounds felt they'd been only slightly more likely to hear from Obama's campaign than Romney's.
But these super PAC turnout operations were largely new and untested compared with the Obama machine and veteran union allies. Even with aggressive outreach to voters, both they and the Romney campaign were ultimately less likely to actually reach voters than the Obama team.
And in an election where swing state percentage gaps between the two candidates were in the single digits, even the slimmest gains along the margins loomed large. Record-breaking numbers of voters cast their ballots before Election Day this year -- half the voting population or higher in some states -- and the Obama campaign was able to bank huge leads weeks ahead of the race's final day.
Republicans played down the disparity in field offices and early vote totals. The office and staffer count, they said, were meaningless metrics.
"If we wanted to have as many staff and offices, we could do that," Romney political director Rich Beeson told reporters last month.
But these Obama outposts, no matter how small, weren't just window dressing; they filled a couple of key functions. Since each was staffed with at least one Obama for America staffer, they served as an initial point of contact with the campaign, and a recruitment center for local volunteers. They provided a central location for campaign events, for phone banking and for data collection. And their permanence allowed the campaign to develop vital local insight: to build detailed voter files on potential supporters, field test the best ways to motivate them, and push them to cast their votes weeks before Election Day.
Republicans said those early voting efforts by the president's campaign were just tapping out their support from voters who would have shown up for him in the end anyway -- and that the edge fueled by early voting would evaporate when Republican voters headed to the polls on Election Day. They weren't entirely wrong; a good chunk of those early Democratic votes came from banking ballots from the president's strongest supporters, base voters who would have shown up no matter what.
But that early vote cushion wasn't just cosmetic. It helped create an aura of inevitability on the ground in key swing states. It provided an insurance policy against potential vote loss to Election Day lines and snafus. And instead of devoting valuable home stretch resources to bringing guaranteed votes to the polls on Election Day, the campaign could instead focus on using those hard-core supporters as Election Day foot soldiers, employing the most personal and effective form of voter persuasion to bring less enthusiastic backers to the polls.
"You go as hard as you can until the end. That's what we're going to do until the very end," said Obama campaign manager Jim Messina.
The end in Colorado: a 50%-47% win for the president.