Tommy’s, a barbershop in a wealthy suburb of northern Atlanta, looks like a shrine to the Grand Old Party. Portraits of Republican dignitaries line the walls, and local party candidates fill the windows with campaign placards.



“I run those Democrats off; tell them what I feel about them,” joked the owner, Tommy Thomas, who has been trimming Republican hair for 44 years. It was 7.30 on Monday morning and, as he spoke, Thomas was gently combing the head of Jack Kingston, a Republican candidate for Senate.



“This is the epicentre of Georgia politics, right here,” Kingston said. “Look at the wall and see who Tommy’s clients are.”



Nearly all of the men in the photographs were white. So, too, were almost all of the men in barbershop. The only black man was on his knees, cleaning shoes.



Half a century after the civil rights movement began nudging much of the south into the grasp of the Republican party, politics in Georgia remain a black and white issue.



Republicans candidates get as much as 80% of the white vote. Democrats receive upwards of 90% of African American support. That colour divide has, since the early 1990s, enabled Republicans to dominate elections in the predominantly white state.



Yet come November, when either Kingston, a congressman, or another Republican contender, businessman David Perdue, stands for election, they will find themselves going up against a demographic shift that is upending old political certainties.



The pool of Republican-leaning white voters in Georgia is shrinking fast. Meanwhile, Georgia’s population of African Americans, Asians and Hispanics is expanding. And minorities tend to vote Democrat.



There are, of course, exceptions to the colour rule. Thomas, for instance, is – despite his strong Republican affiliation – an admirer of the black Democratic mayor of Atlanta, Kasim Reed.



And he insists a growing number of African Americans are coming to his barbershop declaring themselves Republican – nowadays, he says, as many as one in 10.



But given the rapidly changing electorate in the state, Georgia Republicans will need to do much better with black voters to keep winning statewide elections.



Georgia Democratic Senate candidate Michelle Nunn. Photograph: David Goldman/AP Photograph: David Goldman/AP

Campaign strategy

Six miles south of Tommy’s, a Democratic operation to ride the demographic wave is under way.



Polls show Democratic Senate candidate Michelle Nunn, 47, the daughter of former senator Sam Nunn, neck-and-neck with Kingston and Perdue, who are in the midst of a bruising primary runoff campaign that won’t be decided until 22 July.



Filling a large hall at Nunn’s midtown Atlanta HQ last month, several dozen volunteers were manning a phone bank to tap the growing pool of potential Democratic voters. So many activists had turned up that the Nunn campaign had run out of phones.

Upstairs, Nunn’s campaign manager, Jeff DiSantis, sat behind his wobbly, makeshift desk, and gave the Guardian a detailed explanation of their election strategy. The central focus is mobilising Georgia’s “giant Democratic base” – a large and growing population of mostly African American voters living in Atlanta and other cities.

Unlike other states, such as Kentucky, West Virginia or Montana, where the electorate moves back and forth between both parties, in Georgia voters stick with one. DiSantis said that provides him with a stable target of likely voters.



“Ethnicity is a major predictor of votes,” DiSantis said, adding: “In a state like this, there is a huge number of people where the question is not who they are going to vote for, by whether they decide to vote.”

Under Georgia’s election rules, the winning candidate in November will need to secure at least 51% of voters to win outright and avoid a runoff two months later, in January. Nunn's pollsters calculate that if she can win over swing voters who have traditionally voted Republican, and ensure a large turnout of minorities, she can reach the threshold.



That is in no small part due to Georgia’s rapid demographic changes, caused by a combination of higher birth rates among minorities, people flocking to the metro Atlanta area in search of work and young African Americans who move to Georgia for university and decide to stay after graduation.



Around 500,000 new voters have registered in Georgia since 2006 – a significant rise in a state of roughly 10 million.



The most recent available census figures show that the percentage of Georgia’s population that is not white increased from 37% to 45% between 2000 and 2010. By the completion of the next census, experts believe, Georgia’s population of ethnic minorities will outnumber whites.



“By 2020, I would be very surprised if Georgia was not a swing state in the presidential elections, if not by 2016,” said Alan Abramowitz, a political scientist at Emory University in Atlanta, who studies the political effects of demographic shifts.



But Abramowitz is among many analysts in Georgia cautioning that 2014's election may be one cycle too soon for Democrats to benefit from the state's shifting demographics.



The reason: the people most likely to vote for Democrats are less likely to cast a vote during a midterm election.



Bannock Street

That conundrum is not unique to Georgia. In every competitive Senate race this autumn, Democrats are focusing on driving up turnout among their base, in a sink-or-swim attempt to buck that midterm trend.



Democrats have over the past decade become experts at get-the-vote-out campaigns, exploiting an exponential growth in data about potential voters and applying sophisticated algorithmic technology to identify their likely political leanings and the best way to convince them to vote.



It is a costly enterprise, requiring thousands of well-organised volunteers targeting likely voters, but was a critical element of both of president Barack Obama’s victories. However, this will be the first time Democrats commit so much focus to fieldwork operations in a midterm election.



“It is a dramatic shift of resources, a strategic shift,” said Sasha Issenberg, author of The Voting Lab, a book about data-driven campaigning.



Party bosses insist they will not give up trying to persuade Republicans or undecided voters to support their candidates.



But voter turnout, in every state, is the priority. A Democratic get-the-vote-out effort, stretching across 10 crucial states, from Alaska to North Carolina, is seeking to boost turnout among single women, minorities and younger voters.



The operation is codenamed ‘Bannock Street’ after a Democratic field office in Denver that helped secure the election of Colorado senator Michael Bennet by ensuring an unusually high turnout in 2010.



The push involves the recruitment of 4,000 paid staff and will cost $60m, and is being orchestrated from Washington by Guy Cecil, who was Bennett’s chief of staff and is now executive director of the Democratic Senatorial Campaign Committee.

Of those Senate races being closely contested in November, Georgia has the largest population, and as such will absorb a large portion of Bannock Street’s resources.



The funds are being used to open field offices, fund phone banks and apply the sophisticated technological tools that sift through the kind of rich voter data that, DiSantis said, would not have been available to the campaign four years ago.



Internal modelling conducted by Democrats and shared with the Guardian estimates there are 632,000 “likely Nunn supporters” in Georgia who voted in the 2012 presidential elections after staying at home two years earlier, when total turnout plummeted below 40%.



“We have a huge target of people who have voted at least once for President Obama that might not turn out if this election [in terms of turnout] looks like 2010,” DeSantis said.

Energised base

On paper, Nunn, 47, is the ideal candidate to lead a voter turnout drive, which requires money, for coordination, and an army of willing Democratic volunteers.



Nunn built a career in the non-profit sector, running the Points of Light Foundation, the largest voluntary service organisation in the country. “That’s obviously my experience,” she told the Guardian. “We’re going to run a strong grassroots campaign. We have a giant field operation. And we’re going to have a terrific investment in mobilising volunteers.”



She is also a fundraising powerhouse, having already secured more than $6.5m in campaign donations – more than either of her Republican rivals. Most of Nunn’s money remains unspent, whereas both Kingston and Perdue are being forced to empty their war chests combating each other for their party’s nomination.



DeSantis will manage one of two different campaign strategies, depending on which Republican wins.



If Perdue, 64, a gaffe-prone former CEO of Dollar General, secures his party’s nomination, Democrats will paint him as a Mitt Romney-style plutocrat with a shady corporate history. It is a characterisation they hope will contrast with Nunn's commitment to public service.



If Kingston, 59, who has represented a congressional district incorporating the city of Savannah since 1993, wins the runoff, Nunn’s team will seek to characterise him as a Washington insider. Nunn, on the other hand, will claim to be an outsider, untarnished by the political fray.



In different ways, Nunn can define herself in opposition to either Republican, without adopting any overtly different policy positions.



That may be crucial if she is going to lure white voters who have in the past voted Republican. To win in November, her team believes she will need to increase the Democratic share of the white vote to 30%.



That is no easy task in a deeply evangelical state, and one in which the seat is being vacated by Saxby Chambliss, one of the GOP’s most conservative senators.



Nunn’s tactic, therefore, is to emphasise what her campaign manager calls a “non-political profile”. As a newcomer to politics, she has no voting record to defend and, perhaps more than any other Democrat running for Senate this November, can distance herself from the Obama administration.



The Points of Light Foundation that Nunn ran has strong historical ties to former president George Bush Sr, a point repeatedly emphasised in her TV ads, which have been ridiculed by opponents who say she is virtually running as a Republican.



That might be smart politics: Nunn has exerted robot-like control on the campaign trail to avoid association with Obama. Cross-examined by the Guardian, the candidate refused to say whether she would have voted for the president’s flagship healthcare law and, asked who was the better president – Obama or Bush – she declined to say.



But there is the rub for the Nunn campaign. To court conservative white voters, Nunn is avoiding the kind of rhetoric that might inspire her base, much of which still supports Obama's historic presidency.



Twenty miles south, on the black side of Atlanta, veteran Democratic activist Pat Pullar has been trying to overcome that contradiction.



The 62-year-old former deputy director of Georgia’s Democratic party, Pullar has decades of experience training volunteers in how to increase turnout. Activists like her are likely to be pivotal for the Nunn campaign.



Boosting turnout is an enterprise Pullar nicknamed “grab and drag” – grabbing potential Democratic voters at shopping malls, churches and train stations, and dragging them, quickly, to a polling booth.



It is a process, she explains, that begins weeks if not months in advance, as party volunteers help register likely Democratic voters and encourage them to submit early voting ballots.



She admits to having trouble rallying support for Nunn among some sectors of the African American community. “They're saying: 'Oh, she's not visiting us, she's not saying she's a Democrat',” she said.



Pullar has been hitting back, hard, giving others a lesson in realpolitik. “That whole Obama, Pelosi, feelgood Democrat thing, works in New York and Illinois. It don’t work in Georgia – we can't do that,” she said. In order to win, Nunn, she added, has to to be “very conservative, like her father was”.



Pullar chairs the Clayton County Democratic party, arguably the most important local party division in Georgia. Clayton County – population 260,000 – has been on the frontline of the state's changing demographics.



The evidence of transformation is everywhere. The school closest to where Pullar lives, Morrow High, has gone from being almost exclusively white, when she moved to Georgia from New York in 1988, to being predominantly black. She recently helped elect city councilwoman Hang Tran, the first Asian American to sit on the local council and the first Vietnamese woman to hold elected office anywhere in Georgia.



In the 10 years leading up to 2010, the number of white people living in the county dropped by 41,000. During the same period, the African American population grew by 50,000, and today African Americans are more than 66% of the county’s residents. The Hispanic population doubled.



If Nunn is going to win in November, she’ll need a higher than average turnout in counties like these. Asked how locals would be inspired to vote for such a centrist candidate, Pullar shrugged and replied: “You just got to have cheerleaders like myself going around the state, talking her up.”



The night Nunn secured her party’s nomination, winning 75% of the vote, her victory rally, at the Sheraton hotel, encapsulated the paradox of her campaign.



Before she appeared on stage alongside her father, speakers warmed up the crowd with the invigorating soul classic Midnight Train to Georgia.



But her speech, directed more to the TV cameras than the room full of campaigners, was devoid of any of the leftwing causes that typically energise Democratic activists. Nunn made no mention of her party affiliation, making a few cautious remarks about dissolving gridlock in Washington and tackling the nation’s long-term debt.



“You know what I thought of the speech?” said a black female activist in the audience. “She didn’t say anything. But maybe that's what she needs to do to win.”