Fredreka Schouten and Christopher Schnaars

USA TODAY

WASHINGTON — A small band of ultra-wealthy hedge fund managers is pumping last-minute donations into newly organized super PACs to help tip the U.S. Senate to Republicans, new campaign filings show.

Bob Mercer, co-CEO of Renaissance Technologies, donated $2.5 million to a new super PAC, Freedom Partners Action Fund, aligned with the conservative billionaires Charles Koch and David Koch. The group has spent $12.3 million in recent weeks to help Republicans in eight hotly contested Senate races. Mercer sent $500,000 late last month to another new PAC, dubbed B-PAC, aiding GOP Senate candidates in Iowa and Michigan.

A newly minted super PAC aiding Republican Joni Ernst has raised nearly half its $1 million haul from two hedge fund billionaires — Elliot Management's Paul Singer and Julian Robertson of Tiger Management. The super PAC, Priorities for Iowa Political Fund, was launched in September and began its spending on her behalf this month.

Republicans need to pick up six seats to take control of the Senate.

"There has been a significant increase in the number of Wall Streeters who would like to see a change of control in the Senate, and my sense is that they are supporting it with their dollars, and they will support it with their votes and the votes of those they can influence," said Lewis Eisenberg, a private-equity executive and a veteran Republican fundraiser.

Normally, economic and fiscal concerns are paramount for the sector, he said. "Today, there is equal concern, maybe even greater concern, about security issues and foreign policy, or lack thereof."

Mercer is among the biggest Wall Street players helping Republicans. He has contributed more than $6.9 million to super PACs and other political action committees in the 2014 election cycle. He declined comment through an aide.

The pro-Ernst super PAC, Priorities for Iowa Political Fund, is among a slew of groups coming to life in the final weeks of the campaign — some with limited disclosure on who underwrites their efforts.

The Committee to Elect an Independent Senate, for instance, has spent nearly $540,000 to aid Greg Orman, an independent seeking to topple Republican incumbent Sen. Pat Roberts in Kansas. It has not disclosed the source of any of its funding. The group's treasurer, Thomas Layton, is the former CEO of the online restaurant reservation site OpenTable. Attempts to reach him through a spokeswoman were unsuccessful.

B-PAC, which has spent more than $1.1 million to aid Ernst and Michigan Republican Terri Lynn Land, accepted $250,000 from New York real estate investor Ben Heller and five members of his family, all of whom listed post office boxes in Washington or Alexandria, Va., as their addresses in Federal Election Commission filings. Heller did not respond to a telephone message Friday.

Democrats also benefit from last-minute cash infusions.

On Sept. 24, former New York City mayor Michael Bloomberg donated $350,000 to Georgians Together, according to campaign reports out this week. The same day, the group reported spending $400,000 on advertising to help Georgia Democrat Michelle Nunn's Senate campaign in her battle with Republican David Perdue.

Super PACs can accept unlimited amounts of money but are barred from coordinating directly with the candidates they support.

Sheila Krumholz, who tracks political spending at the non-partisan Center for Responsive Politics, said the "new groups can come from nowhere and change the outcome of a competitive race."

Some donors, who may have been holding back, "are reading the tea leaves and deciding to jump in," she said.

Follow @fschouten on Twitter.