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This story was originally published by The Center for Public Integrity, a nonprofit, nonpartisan investigative news organization in Washington, D.C.

In a striking departure from the 2012 election, super PACs and other non-candidate organizations have spent more on U.S. Senate races in July, August and September than on the presidential election, a new analysis shows.

The spending pattern may be the best evidence yet that the big money that would normally go to supporting the GOP frontrunner has instead migrated down ballot, especially to U.S. Senate races where there is a strong chance Democrats may take control.

The Center for Public Integrity analyzed campaign finance data from the nonpartisan Campaign Finance Institute.

Donald Trump, the Republican presidential nominee, at least initially showed disdain for super PACs, but has since changed his position and has actively courted them.

And yet, no group dedicated primarily to supporting Trump’s presidential candidacy ranks among the top 15 biggest spenders among super PACs and similar political groups, according to the Center for Responsive Politics.

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Meanwhile super PACs supporting Senate and even House candidates are flush with cash as the Nov. 8 election looms.

Smart money bet?

Travis Ridout, a co-director of the Wesleyan Media Project, which tracks advertising in federal elections, said donors may just be attempting to spend their money wisely.

"When one [presidential] candidate is ahead by 6 percentage points, it just doesn’t make all that much sense to try to invest hundreds of millions of dollars," he said. "Whereas you’ve got a Senate race in, take Missouri, which looks to be within 2 percentage points. There’s a race where advertising could have an impact and it’s going to cost you a lot less to have an impact."

The Wesleyan Media Project reported that, as of late August, involvement in Senate races by "outside" groups — they include political action committees, super PACs, labor unions, trade associations and social welfare nonprofits, including "dark money groups" that aren’t required to disclose their donors — had reached an all-time high, accounting for nearly 50 percent of TV ads to that point.

As a whole, as of mid-October, the number of presidential ads run by candidates, political parties and outside groups such as super PACs was less than half of what it was in 2012.

The 2016 presidential election stands in significant contrast with the 2012 election, the first election after the Supreme Court’s 2010 decision in Citizens United v. Federal Election Commission, which unleashed gushers of outside money into federal elections.

In 2012, Restore Our Future, the main super PAC dedicated to supporting Republican presidential candidate Mitt Romney, ranked second on the list of highest-spending super PAC and nonprofit groups.

Only the combined spending of the Karl Rove-backed super PAC American Crossroads and its related nonprofit, Crossroads GPS, eclipsed Restore Our Future. The two Crossroads groups together spent about $114 million to boost Romney and bash President Barack Obama.

No help for Trump

Flash forward to Election 2016. Restore Our Future has all but shuttered its operations and hasn’t spent a dime helping Trump. The two Crossroads groups are veritable nonentities this presidential campaign, spending less than $140,000 on messages attacking Democratic presidential candidate Hillary Clinton.

Matters are much different down the ballot. Surges in contributions to congressionally focused conservative super PACs have tracked some of Trump’s dips in the polls, suggesting his performance at the top of the ticket has spurred the flow of resources into congressional races.

Take the conservative Senate Leadership Fund, a super PAC that has largely superseded its sister Crossroads organizations. It raised $2.6 million in July. It then raised $28.2 million — more than 10 times as much — in August.

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Coincidence? Unlikely. August was a rough month for Trump that included, among other things, a war of words with the Muslim parents of Capt. Humayun Khan, a fallen American war hero.

Senate Leadership Fund leader Steven Law announced an additional $25 million in spending on October 25, fueled by late donations and aimed at seven competitive Senate races. Senate Leadership Fund has pulled in seven-figure checks from major Republican donors who aren’t spending any money to support Trump, including New York investor Paul Singer, Arkansas investment banker Warren Stephens and Blackstone Group CEO and Chairman Stephen Schwarzman.

The boost came after panicking Republicans saw Democrats were shifting resources from the presidential election to the fight for control of Congress. Democrats were emboldened by Trump’s sinking poll numbers and the reaction to a newly released "Access Hollywood" tape from years ago that caught Trump lewdly describing how he might sexually assault women. (Trump has downplayed his comments, calling them "locker room talk.")

Republican donors were also motivated by stories that suggested Republicans were on the verge of being outspent in key Senate races, as they fought to maintain control of Congress’ upper chamber in a year where the battleground map was already viewed as friendlier to Democrats.

Republicans have made their move "especially in the last two weeks," said Ian Prior, a spokesman for the network of groups that includes the Senate Leadership Fund, the New Hampshire-oriented super PAC Granite State Solutions and the nonprofit group One Nation.

Senate Leadership Fund’s most recent filing showed an $11 million contribution from One Nation, which is not required to reveal its donors.

‘Dark money’ deluges Senate races

A search of records maintained by the FEC shows it appears to be the largest single ever contribution by a so-called "dark money" group to a super PAC. Super PACs may raise and spend unlimited amounts of money and must disclose their donors. But they’re permitted to accept money from nonprofit groups that don’t.

One Nation has itself spent $3.4 million on what it describes as postage, printing and production costs backing Republican Senate candidates in Indiana, Missouri, North Carolina, New Hampshire, Pennsylvania and Nevada.

In addition, according to a report released by the Center for Responsive Politics and the Wesleyan Media Project, the group spent more than $23 million running so-called issue ads in Senate races earlier this election cycle. Because the ads aired more than 60 days before the election and didn’t explicitly ask viewers to vote for or against a candidate, they did not have to be reported to the Federal Election Commission.

On Wednesday, Senate Leadership Fund announced it was beginning a new $2 million ad campaign in Wisconsin.

Meanwhile, Priorities USA Action, the flagship super PAC supporting Clinton’s presidential bid, is the top spender among all super PACs this cycle. It has poured more than $117 million into the election so far, with the overwhelming amount used to promote Clinton or attack Trump.

Such spending is almost twice what the super PAC spent in 2012, when it helped Obama win re-election.

While still mainly concentrated on the presidential race, Priorities USA Action is also running TV ads to boost congressional candidates in three races: Iowa’s first House district and the New Hampshire and Pennsylvania Senate races.

This is because many Democrats believe Clinton’s perceived lead in key battleground states afford them the luxury to divert resources toward congressional races.

"While our main goal has always been and continues to be ensuring Hillary wins in as many places as possible by as much as possible, we also want to surround her with Democrats in Washington that can help move the country forward," said Justin Barasky, a spokesman for Priorities USA Action.

Democrats' pro-Senate super PAC

Barasky said Clinton is running strongly in those areas, and the group decided to use the already reserved airtime to "make a difference in a down-ballot race."

Senate Majority PAC, the primary outside spending group concentrated on Senate races for the Democrats, has seen its receipts steadily climb and reported a new high of $19.3 million raised from Oct. 1 to Oct. 19.

Democrats, like Republicans, have been boosted by nonprofits that keep donors secret.

Majority Forward, a nonprofit group formed in 2015 that has been described as an affiliated organization that shared office space and staff with Senate Majority PAC, has paid Senate Majority PAC nearly $700,000 for salary, rent and insurance expenses so far this election cycle.

In addition, Majority Forward has spent $9.4 million on television and radio ads to aid Democratic candidates, according to reports filed with the FEC, almost all in connection with Senate races in Pennsylvania, Nevada, Missouri and North Carolina. About two-thirds of that money has been spent since Sept. 29, the reports show.

Majority Forward has also spent millions of dollars on ads that don’t have to be reported to the FEC.

The burst of Democratic spending is causing heartburn for operatives working to keep the Senate in Republican hands.

"I worry every day, and every day it’s a different state," said Scott Reed, the senior political strategist for the U.S. Chamber of Commerce. The Chamber has spent $32 million boosting Republican congressional candidates, according to FEC filings.

But in October, two weeks before the election, Reed found himself watching Trump taking time to attend an event at his new hotel in Washington, D.C., while vice presidential nominee Mike Pence headed to a rally in Utah, a state Republicans haven’t lost in decades.

"You couldn’t make it up," he sighed.

The U.S. Chamber, which doesn’t intervene in presidential elections, is now concentrating on Senate races in six states: Nevada, North Carolina, Missouri, Indiana, Pennsylvania and New Hampshire.

"The Access Hollywood tape kicked it into high gear," Reed said of donor interest in the Chamber’s congressionally focused efforts. "Three weeks ago, we saw a big spending deficit in these six key states and I can tell you…we’re almost at par."

Reed said he’s turned his efforts to voter turnout.

Heather Hargreaves, vice president of the national program at NextGen Climate Action Committee, the liberal super PAC funded by billionaire environmentalist Tom Steyer focused on climate change, said her group has focused its effort on field work this cycle.

NextGen, which reported receiving $66 million from Steyer so far this election cycle, has spent a total of about $52 million, Hargreaves said. About $31.5 million has been spent on Senate races, and the rest on the presidential contest.

The group has thrown its support behind candidates it considers "climate champions," she said, including Clinton and an array of Senate candidates. It has worked to educate voters on candidates’ positions on issues, primarily climate change, she said, and is employing digital methods such as text messaging to reach millennial voters.

"What’s important right now is getting millennials to the polls," she said.

The Center for Public Integrity is a nonprofit, nonpartisan investigative news organization in Washington, D.C.