The most expensive U.S. Senate race in history is unfolding in Pennsylvania, where Wall Street, unions and billionaire industrialists Charles and David Koch are flooding the state with money.

At least $139 million has been spent by advocacy groups and the candidates, Republican incumbent Pat Toomey and Democrat Katie McGinty, Federal Election Commission filings show. The money has paid for legions of door-to-door canvassers and about 449 hours of negative television ads over the past six months.

The record spending shows that both parties see Pennsylvania as pivotal in the all-out battle for the Senate. Of the 34 open seats this year, it’s one of six that are considered a statistical toss-up, according to RealClearPolitics polling averages. On top of that, Toomey’s place on the Senate committees that oversee banks and tax policy raises the stakes for the financial industry and other corporations.

The biggest source of money in the race is the Democrats’ super-PAC, the Senate Majority PAC, which has spent about $19.9 million so far. Its Republican counterpart, the Senate Leadership Fund, has spent about $11.7 million. Casino magnate Sheldon Adelson gave the group $20 million in August.

Banks, Hedge Funds

There are 18 other groups that have spent more than $1 million on the race. Among those supporting Toomey are the Kochs’ Freedom Partners Action Fund, the U.S. Chamber of Commerce, and Club for Growth Action. Others, including Majority Forward, Women Vote!, and Planned Parenthood’s political arm are backing McGinty.

Employees from banks, hedge funds and private equity firms have given about $4.6 million to Toomey’s campaign and two allied committees. McGinty has taken in $361,120 in donations from those groups. Toomey, a former president of free-market advocate Club for Growth, worked in finance, including a stint as a derivatives trader, before embarking on a political career. If he were to lose, it could leave the industry with fewer allies on the committee that shapes financial regulation and vets key appointments at agencies like the Treasury Department and the Securities and Exchange Commission.

His ties to Wall Street have formed McGinty’s main line of attack. She has aligned herself with Senator Elizabeth Warren, who is loved by progressive Democrats for being a consistent and vocal critic of banks. McGinty joined Warren on a September conference call with reporters to chastise Wells Fargo & Co.’s former chief executive officer, John Stumpf, after the company was found to have created millions of bogus accounts without customers’ knowledge. On the call, the women pledged to work together to stop legislation supported by Toomey to gut the Consumer Financial Protection Bureau, one of the agencies that sanctioned Wells Fargo. McGinty has continued to bring up Wells Fargo and the CFPB on the campaign trail.

“Either you believe that those who would defraud innocent consumers should be held accountable –- as Senator Warren and I do –- or you focus on reducing the chances that fraudulent behavior comes to light and is rooted out -- as Pat Toomey does," McGinty said in an e-mailed statement to Bloomberg News.

Double Whammy

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