In the aftermath of Tuesday's Republican U.S. Senate primary in Nebraska, campaign finance watchdogs are concerned about the role businessman Joe Ricketts played in helping underdog state Sen. Deb Fischer secure the GOP nomination.

Ricketts, the founder of the Omaha-based online brokerage firm TD Ameritrade, was behind a $250,000 last-minute super PAC ad buy designed to boost Fischer's prospects in a three-way race that also featured frontrunner Jon Bruning, the state's attorney general, and state Treasurer Don Stenberg, the favored candidate of the conservative Club for Growth and tea party-aligned Sen. Jim DeMint (R-S.C.).

Thanks to this spending surge and an eleventh-hour endorsement from former Republican vice presidential candidate Sarah Palin, Fischer garnered more than twice as many votes as Stenberg -- and beat Bruning by 5 percentage points. Her upset came after she raised only about one-eighth of Bruning's $3.6 million haul.

If she prevails in November against Democrat Bob Kerrey, a former Nebraska governor and U.S. senator, watchdogs worry Ricketts' influence would be considerable.

"I don't think there is any doubt Ricketts will get more access to Fischer than regular Nebraskans," said Adam Smith, communications director at Public Campaign. "This is about electing politicians that will benefit his bottom line and the TD Ameritrade lobbyists will know they have a likely champion if she's elected in November."

This concern is echoed by Meredith McGehee, policy director at the Campaign Legal Center, which, like Public Campaign, favors campaign finance regulations.

"Washington is responsive to the people who got them in power," said McGehee. "You know the old saying, 'He who pays the piper calls the tune'? That's the system we have."

Ricketts' super-sized contributions to a political group that ran ads advocating against Bruning and for Fischer are legally allowed in the wake of the U.S. Supreme Court's 2010 Citizens United ruling. Previously, individuals were limited to giving just $5,000 per year to groups that made "independent expenditures," the Federal Election Commission's term for messages that explicitly tell people to vote for or against a candidate.

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