Fredreka Schouten and Christopher Schnaars

USA TODAY

WASHINGTON — Big sums are flowing into the coffers of presidential contenders Hillary Clinton and Donald Trump, but the super wealthy also are pumping huge amounts into the outside groups that are scrambling to influence the White House race and determine which party controls the Senate, new reports show.

A pro-Clinton super PAC, Priorities USA Action, raised $23.4 million in August, its largest monthly haul of the campaign, according to a report filed Tuesday with the Federal Election Commission.

In all, 11 people wrote seven-figure checks to Priorities last month, accounting for nearly 80% of its total receipts in August. Its top donors include Democratic stalwarts, such as Chicago media executive Fred Eychaner and Slim-Fast founder S. Daniel Abraham who each gave $3 million. Billionaire financier George Soros, donated $2.5 million, and Emerson Collective, a limited liability company founded by Laurene Powell Jobs, donated $2 million. She is the widow of Apple's Steve Jobs.

Other Silicon Valley billionaires are helping Democrats.

Facebook co-founder Dustin Moskovitz and his wife Cari Tuna recently pledged $20 million to help Clinton and other Democrats and Tuesday’s filings showed them starting to write those big checks. The couple donated a combined $5 million to the League of Conservation Voters on Aug. 22, accounting for most of the $5.9 million the group collected last month.

But the filings also show the super wealthy directing big cash to downballot contests, particularly the Senate where Republicans hold a narrow majority and are defending 24 seats in November to Democrats’ 10.

Las Vegas billionaires Sheldon and Miriam Adelson, who were the largest super PAC donors of the 2012 election, began opening their wallets in August, contributing $20 million to the Senate Leadership Fund.

That accounts for the lion’s share of the $28 million the group raised last month as it works to preserve the Republican Party’s majority in the Senate. Hedge-fund manager Ken Griffin donated $2 million to the super PAC, which is closely aligned with Senate Majority Leader Mitch McConnell, R-Ky.

Sheldon Adelson also directed funds to a specific race, giving $1.5 million to Granite State Solutions, a super PAC working to protect endangered New Hampshire Sen. Kelly Ayotte, new reports show. Ayotte, a first-term Republican, is locked in a tight race with the state’s Democratic Gov. Maggie Hassan.

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A Democratic group focused on seizing the Senate from Republicans harvested big sums, too. Senate Majority PAC soared to its best fundraising month of the cycle last month, taking in $11.6 million. Its largest donation: $1.25 million from Alexander Soros, George Soros’ son.

All this money is helping to drive big spending in Senate contests.

The proportion of Senate ads sponsored by outside groups last month reached an all-time high, according to an analysis released Tuesday by the Wesleyan Media Project.

Republican groups have sponsored nearly 52% of all the TV ads aiding GOP candidates, up from 49% in the 2014 midterm elections. Democratic groups have sponsored about 40% of the pro-Democratic Senate ads, roughly on par with spending two years ago.

Pro-Republicans groups “are putting more energy into the race for the U.S. Senate than they are for the White House,” said Michael Franz, co-director of the Wesleyan Media Project.