CLEVELAND/MIAMI (Reuters) - From the outside, it looked like an abandoned storefront in a run-down part of Cleveland. But inside, dozens of supporters of President Barack Obama gathered on a recent Sunday for an event that was part political rally, part religious revival.
"Gotta vote" signs hung from the ceiling and smoke from an outside grill wafted through the room. Hot dogs, buns, chips and sugar cookies were laid out on a table for the volunteers, most of whom were African-American.
"God is not going to allow this man to fail, because of people like you," radio host Yolanda Adams told the volunteers who had gathered to make calls and knock on doors, encouraging neighbors to register and then vote for Obama.
"You're making the world a better place by saying, 'Hey, have you registered?' " Adams said to shouts of, "That's right!" and, earlier in her remarks, "Amen!"
If Obama holds off his Republican rival Mitt Romney in the crucial state of Ohio and goes on to win a tight race, it could be thanks to roughly 120 such field offices across the state - and hundreds more nationwide.
They are home to an Obama "ground game" operation that is sophisticated in identifying potential supporters yet basic in relying on personal contact from neighbors to register potential voters and help get them to the polls.
Democrats say the breadth of Obama's organization is unprecedented in national politics - a claim that draws skepticism from Republicans, who have built a large get-out-the-vote operation of their own.
One thing is clear, however: Obama's organization - which his campaign says involves hundreds of thousands of people nationwide - reflects the power of incumbency.
Some of Obama's local offices never closed after the historic 2008 election that made him the nation's first black president. As a result, Obama is viewed even by some Republicans as having an advantage in on-the-ground organization, the trench-warfare part of a national campaign.
That is especially crucial now, with early voting under way and the campaigns blanketing key states such as Ohio, Florida and Virginia with television ads.
Obama needs such edge at a time when the economy, although showing signs of life, continues to struggle. His lackluster performance in his first debate with Romney on October 3, which gave the Republican a lift in the polls, has increased the urgency for results from the operation built by Obama campaign manager Jim Messina.
"We've got a stronger organization on the ground than we did in 2008," said White House adviser David Plouffe, Obama's campaign manager four years ago. "What Jim's built here is ... going to break new ground organizationally and technologically."
Messina told the Democratic National Convention five weeks ago that the campaign and its supporters had made 43 million calls and registered more than 1 million voters, more than Democrats registered in 2008.
Republican officials, alarmed by Obama's operation, have made a point of building the party's most extensive ground organization to date. Since Romney clinched the Republican nomination in the spring, nearly 108,000 volunteers nationwide have made close to 40 million "voter contacts" and knocked on about 7.5 million doors, a party official said.
"Our ground game is better than their ground game," said Rick Wiley, political director for the Republican National Committee, who questioned why Romney folks were not crossing paths with Obama's volunteer army.
"When you knock on 4 million doors in battleground states, you would think that our ... volunteers would run into the Obama folks," Wiley said. "But we're just not seeing them."
Wiley's comment could be political gamesmanship, but the voter-targeting tactics used by each side could help explain why many Obama and Romney volunteers do not cross paths.
The campaigns often focus on areas that are solidly Democratic or Republican to try to make sure reliable party supporters go to the polls.
At a phone bank in the Toledo area a day after the Cleveland canvassing event, Obama volunteers worked through long lists of people in surrounding neighborhoods. Signs on the walls encouraged them not to leave messages, not to read scripts mechanically and not to stay on the phone too long.
Volunteer numbers are rising, and a bell rings in the office when a call recipient agrees to become an Obama volunteer. Not all of the calls end well for the campaign, though.
"You're undecided, huh?" Maggie Whitman, 80, said to one person on her call list. She encouraged the voter to tune in to the first presidential debate - the one in which a subdued Obama did not fare so well.
Republicans say their ground game has improved after Romney's debate performance, with new volunteers showing up at campaign offices and more people seeking yard signs and bumper stickers to support the former Massachusetts governor.
No Republican has ever been elected president without winning Ohio, which has 18 of the 270 electoral votes needed to clinch victory in the state-by-state race for the White House. The RealClearPolitics average of recent polls has Obama leading in Ohio by less than 2 percentage points.
The campaigns and their allies have spent millions of dollars this year on research about voters and their tendencies.
Among other things, the campaigns have used demographic reports from companies that track consumers' spending habits and social network activity to help identify "unlikely voters" - those who probably will not cast a ballot in the November 6 election and rarely have in previous elections.
For unlikely voters, personal contact from a campaign staffer can be key to reinforcing the notion that their vote matters and that it is worth their time to vote.
"Sophisticated campaigns know that there are voters who, if they are left to their own devices, they won't turn out," said Christopher Mann, a political scientist at the University of Miami. "Changing that behavior and getting those people to the polls is what it's all about."
At the meeting in Cleveland last month, Obama volunteers got tips on how to bring more people into the Democrats' fold.
"We want to remind you that felons can vote - past felons, current, (and) waiting-to-be-sentenced," said Eletrice Harris, an Obama staff member, referring to Ohio's law that prevents felons from voting only if they are behind bars on Election Day.
"We need to get them registered," Harris said, "because if they are not incarcerated on November the 6th, they can vote."
Felons, of course, make up only a tiny portion of the electorate that the Obama campaign is targeting.
Obama's Chicago-based team is trying to make up for Romney's big lead among white men by making appeals to several other groups, including women, Hispanics and young voters.
Labor unions, a Democratic stronghold, have helped Obama's campaign by registering 68,181 new union voters in Ohio and 450,000 nationwide since March 2011, according to the AFL-CIO.
Obama's campaign has invested heavily in Ohio; its roughly 120 offices there are more than it has in any other state. Romney's team, which has 40 offices, casts the Obama group's focus on office numbers as a public relations ploy.
"I'm not interested in building an organization for the sake of public relations," said Scott Jennings, Ohio state director for Romney's campaign. "I'm interested in building an organization for the sake of voter contact."
But Jennings acknowledges that the Democrats' head start in building a ground network gave them an advantage.
"The advantage of being an incumbent president is that you can start early," Jennings said, calling what the Republican team has built since last spring "incredible."
For both campaigns, a priority of the ground game is to lock in the support of those who vote early or by absentee ballot.
A Reuters/Ipsos poll on Sunday indicated that Obama held a significant lead among those who have voted early so far.
Such positive signs for Democrats on early and absentee voting might not necessarily lead to victories.
In Florida, another coveted state where both campaigns are battling on the ground and the airwaves, the Obama campaign's ground game is bigger and better organized than it was in 2008.
Democrats in the state point to reports that they have nearly matched Republicans in the number of people voting absentee. In the 2008 election, the Republican advantage among such voters was 16 percentage points.
But recent polls have indicated that Romney could be building a lead in Florida. The RealClearPolitics average of polls gives the Republican a lead of nearly 3 percentage points in Florida, which is worth 29 electoral votes to the winner.
Obama's ground game in Florida has three weeks to try to reverse Romney's momentum before the November 6 election. The battle will be fought by Obama volunteers such as Eric Varsallo, a team leader in the campaign's office in the Midtown section of Miami.
Varsallo said volunteers run into a lot of apathy from people who "don't feel that their votes count."
But he says an in-person conversation with a campaign volunteer can change that.
"When they see our positive energy and how we believe in it, it rubs off," he said. "It's contagious."
Mason reported from Ohio, Adams from Florida; Editing by David Lindsey and Cynthia Osterman