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By Jacob Pramuk, CNBC

A super PAC pushing for a Republican Senate majority saw a fundraising rush in the U.S. election's final days, partly driven by GOP megadonors from the business community who were wary of then-candidate Donald Trump.

The Senate Leadership Fund raised $39.7 million from Oct. 20 to Nov. 28, just shy of 40 percent of its haul for the entire election cycle, according to a Federal Election Commission report filed Thursday. All of those donations came by Nov. 7, the day before the election.

The Senate Leadership Fund announced its plans Oct. 5 to pour an additional $25 million into Senate races, an impressive amount in the final days of an election.

Wall Street tycoon Stephen A. Schwarzman attends a ground breaking ceremony for a residential college building on the grounds of Tsinghua University in Beijing, China, Thursday, Oct. 24, 2013.Ng Han Guan / AP

Billionaire Las Vegas Sands CEO Sheldon Adelson and his wife Miriam donated most of the last-minute haul, giving a total of $15 million on Oct. 24, while billionaire Blackstone CEO Steve Schwarzman contributed $2.2 million a day later. Hedge fund manager Paul Singer of Elliott Management chipped in $2 million on Oct. 26. Singer, who once said Trump's policies would lead to a global depression, has warmed to him more since his election. He attended a fundraising breakfast for Trump this week and plans to donate to his inauguration.

On Oct. 21, a $9.2 million contribution came from the Senate Leadership Fund's sister organization, One Nation, a 501c4 that does not have to disclose its donors.

The haul from business giants came as Republicans looked to cling to a Senate majority as polling showed an advantage for Democratic presidential candidate Hillary Clinton and the potential for a Democratic Senate takeover. But a better-than-expected turnout for Trump propelled him to a win and helped Republicans keep control of both houses of Congress, with Democrats gaining only two Senate seats.

The Senate Leadership Fund reported about $38 million in independent expenditures, or political communications for or against a particular candidate, during that period. It bought media opposing Democratic candidates in key states including Pennsylvania, Florida, New Hampshire, North Carolina, Nevada and Missouri.

Las Vegas Sands Corporation Chairman Sheldon Adelson speaks to students at the University of Las Vegas, Nev., in Las Vegas, in April 2012.John Locher / Las Vegas Review-Journal via AP file

Democrats only beat Republican incumbents in New Hampshire and Illinois.

Adelson and Singer, huge Republican donors in the past, shied from Trump in this cycle but still contributed to other Republican causes. Schwarzman, who has been less active as a donor than Adelson or Singer, will head a forum that will advise Trump on business policy.

A Democratic PAC, the Senate Majority PAC, raised $18 million in that same period, less than half of its Republican counterpart. It spent just over $23 million on independent expenditures.

Leigh Ann Caldwell contributed.