Now, what to do with all of those 13 million e-mail addresses?

With President Barack Obama settling into the White House on Tuesday, his political apparatus appears to be exploring an unprecedented digital way station for his campaign’s database of donors and grass-roots supporters.

In a recent interview with the Washington Post, Obama’s campaign manager, David Plouffe, confirmed that he is organizing a new grass-roots organization made up of former campaign volunteers to “organize their own communities, their own towns” around the new administration’s goals.

“It’s never been done before, at least at this scale,” Plouffe said. “We’ll have some staff, but it won’t be as rigorous as the campaign, so we’re really going to have to rely on volunteer team leaders around the country.”

But Plouffe, who did not respond to Roll Call interview requests, was quick to remind the Post that “this is not a political campaign,” perhaps hinting at the legal considerations he and others may face in shepherding a campaign out of the normal realm of politics — and likely back again three years from now.

Maintaining contact with voters after Jan. 20 will have immediate and long-term benefits for the new administration, according to campaign finance lawyer Ken Gross. Obama’s political machine undoubtedly wants to maintain contact with voters in preparation for his re-election bid in 2012 and, in the meantime, encourage supporters to exert pressure on Members of Congress to support the White House’s ambitious agenda.

“You turn them over to a committee that will continue to apprise them of what is going on with the administration,” Gross said. “You want to keep the names current.”

For now, however, little is known about how exactly the new organization would be organized. The Democratic National Committee, a possible administrator for the group, declined to discuss the proposed grass-roots operation, as did the new White House press shop.

Still, campaign finance experts interviewed for this article said one possibility is setting up a group registered under section 501(c)(4) of the tax code, a “social welfare organization” similar to the National Rifle Association or AARP.

But that route, experts say, requires diligent legal oversight, as former aides to then-President George W. Bush found out two years ago.

Following Bush’s win in 2000, his campaign manager, Tony Feather, started up a similar grass-roots effort to push the White House’s agenda. The 501(c)(4) organization, Progress for America, ultimately ended up running afoul of campaign finance laws when federal regulators determined that an affiliated group, Progress for America Voter Fund, failed to register as a political committee and violated contribution limits.

The group, which raised nearly $45 million ahead of the 2004 election, paid a $750,000 fine two years ago.

“Progress for America was seen by the [Federal Election Commission] eventually as a political committee and therefore barred from accepting any soft money contributions,” one Republican campaign finance lawyer warned.

The lawyer also advised the group’s organizers against packing its ranks with Democratic operatives, a move that could draw scrutiny from regulators looking to prove that it was affiliated with other party committees — and therefore, subject to lower federal contribution limits.

“If you’ve got a person or the same group of people controlling two organizations they can be viewed as ‘affiliated,’ which means that they have shared contribution limits,” the lawyer said. “You would not want the 501(c)(4) having a shared limit with the DNC.”

Should Plouffe and other organizers decide to organize the new grass-roots lobbying effort as a nonprofit group, experts claim, it could enter into a “list exchange agreement” with Obama’s political operations. Such an agreement would allow the grass-roots group to keep up-to-date the campaign’s vast catalogue of e-mail addresses and cell phone numbers, which played a crucial role in electing the nation’s 44th president last November.

“You can stagger it, so that the group that is just starting gives [Obama’s re-election committee] the names later,” the lawyer said. “What that allows you to do is it becomes a non-reportable event, there is no in-kind contribution because each side is getting something of equal value, which is important because a nonprofit can’t make an in-kind contribution to a campaign.”

“This group can spend the next three years expanding that list, then the Obama folks get it back for the [re-election],” the source added.

But another campaign finance lawyer, a Democrat, said that there are advantages to registering the group as a political committee. Perhaps most important? Avoiding the ire of the FEC for exceeding contribution limits or failing to register as a political committee.

“Once you’ve raised ‘hard money,’ you can pretty much do whatever you want to do with it,” the Democratic lawyer said. “It’s usually when people try to skirt the rules that they end up getting hung up.”