In-depth coverage of the candidates and the issues, all leading up to the Aug. 5 primary and the Nov. 4 general election.
Clairton, Pa. Five days a week, Linda Graham trolls tattered neighborhoods of this once thriving steel city outside Pittsburgh for unregistered voters she can sign up as Democrats - one of thousands of unknown volunteers whose work outside the limelight has already altered the basic arithmetic of the November election.
The epic nomination battle between Barack Obama and Hillary Clinton helped put millions more Democrats on the voter rolls while Republican registration declined. Now Graham, 45, has taken three months of unpaid leave from her job at Pittsburgh's Central Blood Bank in the hope of adding to those gains before the presidential vote.
To counter this effort, the Republicans are counting on a formidable, high-tech get-out-the-vote operation that has helped them win the past two presidential elections.
Since the last federal election in 2006, volunteers like Graham combined with the enthusiasm generated by the Obama-Clinton struggle to add more than 2 million Democrats to voter rolls in the 28 states that register voters according to party affiliation. The Republicans have lost nearly 344,000 thousand voters in the same states.
The Democrats hope their voter registration efforts can boost Obama to victory in competitive states like Pennsylvania, Nevada and Florida and perhaps give him a shot at winning traditional Republican states like Georgia, North Carolina and Virginia.
Both Obama and his Republican rival, John McCain, are fighting for independent swing voters, and many of the new Democrats had been unaffiliated voters.
The number of unaffiliated voters dropped by nearly 900,000 since 2006. Many joined the Democratic Party to take part in the primaries and caucuses, and now they will now be targeted by an aggressive get-out-the-vote campaign.
"We feel that our supporters are more enthusiastic than we've seen in previous cycles," said Jon Carson, Obama's national field director.
The Obama campaign is taking the lead among the party organizations and labor unions that traditionally work on voter registration efforts.
Because party organizations and unions, like the Service Employees International Union to which Graham belongs, can raise unrestricted amounts of money, presidential campaigns typically rely on them to handle the bulk of voter registration drives, Democratic National Committee chairman Howard Dean said in an interview.
"This is the first campaign I've seen where the voter registration is done by the campaign," Dean said.
The Republicans are relying on a more traditional voter registration model, with the Republican National Committee leading the effort among state parties.
"We hope that the hard work we've done in the past will provide us with a strategic advantage," said Mike DuHaime, McCain's political director. "We will have the most technologically advanced ground operation ever."
DuHaime said the RNC is working with the state parties to register voters in every battleground state. He said there is extra emphasis on the fast-growing ones, including Nevada, Colorado, New Mexico, Florida and North Carolina.
Nationwide, there are about 42 million registered Democrats and about 31 million Republicans, according to statistics compiled by The Associated Press.