The costly Republican primary has been draining Mitt Romney's wallet and giving President Barack Obama time to build an expansive campaign architecture with offices in 45 states and hundreds of employees.

The bad news for Obama is he's had to start paying for all this now.

Obama has spent more than $135 million — more than GOP challengers Romney and Rick Santorum combined — on his re-election apparatus, according to an Associated Press analysis of Federal Election Commission records. That sets up his campaign to be larger and geographically more diverse than any of his opponents' organizations.

Through the first two months of the year, Obama spent approximately $1.1 million on computer equipment, $435,000 on rent and utilities, $305,000 on telephones and $19,000 on office supplies, according to federal reports.

Republican contenders Romney and Santorum have been watching their expenses during the GOP primaries, relying on a fraction of the amount Obama can spend on essentials like ad spending, travel fees and utility bills. But Obama's campaign has its eye on spending by Republican-leaning "super" political action committees, which can accept unlimited and effectively anonymous contributions from billionaires, corporations and others.

Super PACs like American Crossroads, which supports Republicans, and Restore Our Future, which supports Romney, are expected to flood the airwaves with TV ads opposing Obama.

"We're building the largest grass-roots campaign in history," Obama campaign spokesman Ben LaBolt said from Chicago, where the president's re-election effort is based. "You can see it here, but it's really happening in the states."

Of $29.5 million spent on operations since the start of the year, at least one-quarter has gone to fundraising-related expenses like postage, printing and telemarketing — an attempt to attract grass-roots donors who supported then-Sen. Obama four years ago. The campaign spent millions more on expenses like online advertising and consulting, which can be tied to fundraising.

Obama's paid staff exceeds 500, many of whom work in the Chicago office — a figure that makes Republicans bristle.

"I think the campaign is single-handedly trying to lower the unemployment rate by hiring field staff," Romney political director Rich Beeson said. "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."

A review of Obama's balance sheets reveals a small army of paid staffers trying to help the Democratic president win a second term. Campaign filings list more than 330 paid staffers in Chicago and 200 more spread across the country, making for a payroll tab that exceeded $6.3 million during the last two months alone.

The core of Obama's operation is packed into the sixth floor of Chicago's Prudential building, where staffers sit side by side at long rows of tables, working from laptops and cellphones. Colorful college pennants hang from the ceiling, some representing key swing states: the University of North Carolina, Ohio State and the University of Michigan. Need a designer T-shirt or bumper sticker? Two staffers manage a swelling collection of campaign memorabilia for sale.

In one corner, more than a dozen workers field questions from journalists scattered across the country. Elsewhere, others coordinate media appearances for Obama's high-profile supporters. Other staffers focus on fundraising, voter identification, social media and campaign-finance reporting.

Beyond the Windy City, Obama's campaign said it's already opened five field offices in Arizona, a state it expects to be increasingly competitive in the fall. The campaign is also taking advantage of party resources there, relying in part on the state's Democratic Party for staffing, phones and computer equipment, records show.

Obama's operation had $84.7 million in cash-on-hand by Feb. 29. The Romney campaign, which is hardly hurting for cash after raising about $74.8 million, says it's not impressed.

Romney's Boston-based campaign is a fraction of the size of Obama's, although its organization dwarfs its Republican competitors. With around 100 paid staffers, Romney has spent more than $180,000 on rent and utilities since early January in 16 states from Massachusetts to Utah, records show.

Santorum, whose national headquarters was technically a post office box until this month, spent just $19,000 since the beginning of the year on rent-related expenses.

Romney's ability to compete against Obama's growing organization has become a selling point on the trail.

"As Republican primary voters in Illinois, we have an opportunity to look at the field of candidates, and look at them and say, 'Who can go toe to toe not just with Barack Obama, but the Chicago machine that is his operation?'" Rep. Aaron Schock, a top Romney supporter in the state, said recently. "We cannot afford to nominate someone on our ticket who cannot withstand the barrage, who does not have the organizational strength and fortitude to go toe to toe with Barack Obama."

In some ways, Obama's massive campaign is part of what drives supporters to give money to super PACs in the first place.

"As a general rule, the big institutional money goes inordinately to incumbents regardless of party, while outside money plays the role of balancing out the party in power or stopping a specific initiative," said Jonathan Collegio, a spokesman for American Crossroads, the Republican super PAC.

GOP-leaning super PACs have spent more than $50 million on TV ads this election. Crossroads is largely waiting until the general election to spend its money.

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Whatever the case, the Democrats' current financial advantage is something Obama's campaign isn't taking for granted. Obama changed course last month in his criticism of super PACs and began encouraging big-money supporters to give to Priorities USA Action, an independent group working in his favor and run by a former aide.

The Republican Party opened offices in three states this month, with plans to expand to four other states in April.