"It's the big fish in the pond," said Malloy. "There are many less problematic groups, such as homeowners associations, and local chambers of commerce that have no political activity."
Close behind the Chamber in fundraising prowess is Crossroads GPS, a nonprofit with ties to Republican strategist Karl Rove. Together with sister group American Crossroads, a "super PAC," they have raised $56 million.
President Obama and groups such as the Campaign Legal Center have expressed concern that such an organization's main purpose is political campaigning, so it therefore should not be considered an issue-oriented nonprofit organization with immunity from having to disclose its donors.
"Just tell us where the money's coming from," said Vice President Joe Biden. "Why can't the Chamber say, 'These are where the contributions are coming from'? Why can't Karl Rove tell us where the contributions are coming from?"
Still, experts say many of these groups are within their rights under the law to keep their donors private, and that if the White House doesn't agree with the law, it should work with Congress to enact a change.
"Since the IRS permits non-disclosure and we convey that [to our donors], we can't subsequently disclose," said Hanna.