In some key swing states, the campaign already has multiple offices and dozens of staff members.

But that build-out has carried high costs for the campaign, which is spending more than $3 million per month on staff salaries and millions more on computer equipment, rent and utilities and general office costs.

Obama's reelection effort has also spent more than $7 million in this year alone on direct mail and telemarketing efforts aimed at reconnecting with small donors. Coupled with additional expenses on online advertising, polling and political consulting, the Obama campaign is running an expansive — and expensive — effort.

By comparison, Mitt Romney's campaign has about 100 paid staffers and has spent less than half as much as the Obama campaign on rent and utilities.

"I think the campaign is single-handedly trying to lower the unemployment rate by hiring field staff," Romney political director Rich Beeson told the AP. "When they point to the fact about how many people they've got hired and how many offices they've got, they're just trying to distract people from the reality of [how] they're going to have a heck of a time finding people to get out and vote for him."

But while Obama's organization might have a larger footprint, there are still concerns for the president's team. Republican rivals have spent millions on advertisements in key swing states like Iowa, Nevada, Michigan and Ohio, giving the eventual nominee a head start in contests that will swing the election. And Republicans have been far more successful than the president in attracting donors to super-PACs, influential outside groups that can raise and spend money without traditional campaign limits.

Although campaigns aren't allowed to directly coordinate with their super-PACs, the GOP primary has provided a primer for how campaigns and the outside groups can easily work in concert — and within the law. At the end of 2011, President Obama's super-PAC had raised around $2 million, a tenth of the haul of the group supporting Mitt Romney, which brought in over $20 million.

The Obama campaign has also seen high-dollar direct donations lag behind 2008, with half as many individuals giving $2,000 or more to the campaign as last cycle. Despite the fractured Republican field, Romney actually has more big-dollar donations directly to his campaign than does Obama.

Obama's fundraising apparatus has still seen success — as evidenced by his campaign's ability to finance the $135 million build-out. Still, in terms of cash-on-hand, Obama only held about a $10 million dollar lead over Romney at the end of February. According to FEC filings, Obama had about $84.7 million in the bank, versus $74.8 million for Romney.

"We're building the largest grassroots campaign in history," campaign spokesman Ben LaBolt told the AP. "You can see it here, but it's really happening in the states."