WASHINGTON - Big money is pouring into the Pennsylvania race for U.S. Senate.
The conservative Freedom Partners Action Fund early last week launched a new television ad, backed by $2 million, accusing Democrat Katie McGinty of enriching herself at the public's expense and amplifying a key talking point from her Republican opponent, Sen. Pat Toomey.
The Democratic Senate Majority PAC hit back Thursday, announcing $1 million worth of ads painting Toomey as a friend of the National Rifle Association. And then the American Federation of State, County and Municipal Employees, a major labor union, launched a costly TV spot, assailing Toomey's ties to Wall Street - echoing McGinty's attacks.
It will all add to the most expensive Senate race in America. It's only August, but more than $52 million has already been spent on the general and primary election, according to the nonpartisan Center for Responsive Politics.
The eye-popping sum reflects the escalating arms race in political spending, much of it fueled by super-PACs and nonprofits that have thrived since a 2010 Supreme Court ruling paved the way for them to accept donations of any size.
Six- and sometimes seven-figure checks to such outfits now blow away the $5,400 maximum an individual can give directly to a candidate.
So independent groups account for at least $27 million spent in Pennsylvania on this election - more than the total spent by candidates.
Only Ohio's Senate race has seen more outside spending, $33 million.
And more is expected as a growing chorus of conservative donors - fearful that presidential nominee Donald Trump could drag down other Republicans - turn their focus to vulnerable GOP senators, hoping to hold Congress as a buffer against a potential Hillary Clinton administration.
About 70 Republicans have signed a letter urging the party's national committee to steer resources to congressional races and "prevent the GOP from drowning with a Trump-emblazoned anchor around its neck."
Several groups active in Pennsylvania say that's already their aim.
"Saving the Senate is the chamber's top political priority," said Scott Reed, political strategist at the U.S. Chamber of Commerce, which has spent $3.7 million aiding Toomey.
The Koch brothers, conservative industrialists who spend heavily on political causes, have refused to aid Trump.
But they're working hard to reelect Toomey.
Freedom Partners, a super PAC in their network, has spent nearly $4 million on his behalf, campaign disclosures show.
On the ground, the Koch-aligned Americans for Prosperity is stepping up efforts against McGinty. On Tuesday, nine of its volunteers fanned out from King of Prussia, knocking on about 2,000 doors and warning anyone who'd listen that McGinty's support for environmental regulations would harm Pennsylvania businesses, said the group's state director, Beth Anne Mumford.
The group says it has knocked on 21,000 doors statewide and made 486,000 phone calls opposing McGinty.
Its president, Tim Phillips, said Pennsylvanians, "whether they're for [Clinton] or against her, they're going to want a check" on her policies.
From the center, a super PAC founded by former New York Mayor Michael Bloomberg plunked down $1.1 million this month for ads supporting Toomey. Bloomberg, an independent who backs tougher gun control, has praised Toomey's support of broader background checks.
The help in the air war is vital in a sprawling state with six TV markets. Other spending goes to voter registration, phone banks and voter outreach.
Liberals aren't sitting out - even though many, including McGinty, oppose the rules that allow such lavish spending.
Independent groups on the left have outspent conservatives so far, in part because of Democrats' expensive April primary. Super PACs helped McGinty win her nomination and have carried the ad fight on her behalf after the costly primary.
Groups on the right have the edge on TV spending in the general election, according to a Democrat who tracks ad buys, but the on-air battle has been balanced enough that McGinty has surged to a tie or narrow lead in recent polls, despite Toomey's $11 million edge in candidate spending.
"The Senate is vital to our priorities, there's no doubt," said Clay Schroers, national campaigns director for the League of Conservation Voters. The environmental group has spent $1.3 million aiding McGinty, whom Schroers described as a champion of clean air and water.
Nearly $7 million more has come from Senate Majority PAC and EMILY's List, which backs pro-choice Democratic women, according to the Center for Responsive Politics.
Planned Parenthood boasts that Pennsylvania is home to its largest volunteer base, 500 strong. The group is using those numbers for canvassing in Western Pennsylvania, and plans to launch TV ads in the coming weeks.
The dollar counts don't capture the full picture because they don't include political nonprofits that don't have to report spending on issue ads. And much more is expected when campaigns kick into high gear after Labor Day.
Among those waiting is Prosperity for Pennsylvania, a super-PAC led by Toomey's former chief of staff, Mark Dion. It had $1.6 million on hand as of its last report.
The cash deluge - and the prospect of last-minute spending by groups that conceal their donors - worries election watchdogs. "Spending is getting exponentially higher every single year," said Josh Stewart, a spokesman for the Sunlight Foundation.
Toomey and conservatives say limiting campaign donations and outside groups, as Democrats hope, would restrict free speech. He, instead, favors more disclosure.
Democrats, including McGinty, argue that big spending stains the political system, increases the power of rich donors, and alienates ordinary voters.
But even those who oppose the current system say they can't compete if they unilaterally disarm.
"Nobody," Stewart said, "wants to be outspent."