The Unintimidated PAC raised $20 million between mid-April and the end of June, according to filings with the Federal Election Commission.
The Beloit billionaire donated $5 million to the PAC, and Marlene Ricketts, who owns the Chicago Cubs along with her husband, Joe, donated $4.9 million. Joe Ricketts, co-founder of TD Ameritrade, chipped in $100,000 of his own, according to the Associated Press.
The $10 million total from the three donors accounted for half of the PAC’s fundraising.
Hendricks, a longtime Walker supporter, also has been the biggest donor to his three successful elections for governor.
She generated controversy in 2012 when she was recorded in documentary filmmaker Brad Lichtenstein’s film "As Goes Janesville" asking Walker when he would make Wisconsin a right-to-work state.
The clip was recorded Jan. 18, 2011, shortly before Walker introduced the Act 10 budget repair bill that ultimately stripped public-sector unions of nearly all of their negotiating power.
Hendricks asks Walker when he would make Wisconsin a "completely red state, and work on these unions, and become a right-to-work state."
Walker replied that his first step would be to "divide and conquer."
Walker went on to win a recall election that came about after Act 10 and won a third election in 2014, giving him a second term.
During that campaign, Walker often was asked if he supported right-to-work legislation in Wisconsin.
At the time, Walker called it an unnecessary distraction, but after winning re-election, the Wisconsin Legislature in February passed a right-to-work bill that Walker signed.
He now touts the legislation during his campaign speeches for president.
Groups that support Walker also raised $5.9 million from a state committee, Friends of Scott Walker, and an additional $6.2 million from the tax exempt Our American Revival, according to the Milwaukee Journal Sentinel.
Walker’s campaign now is aiming to grow his public profile following the first Republican debate, dominated by controversy generated by Donald Trump. Most pundits rated Walker’s performance as solid, neither hurting nor particularly helping him.
Although he answered more questions than most other candidates, his total time answering questions was near the bottom, indicating a stay-safe strategy.
After trying to avoid being drawn in to a critique of his rival, Walker on Monday said on Fox News Channel’s "America’s Newsroom" that following Trump is like "watching a car accident instead of focusing on the direction we should be headed."
"That’s a sideshow out there," Walker said. "I think most of us as candidates -- at least I do -- I want to be talking about how we make this country great again."
Walker said that Trump is "drowning just about everybody else out."
Unintimidated PAC plans to start spending some of its cash with a TV advertising buy beginning next month in Iowa.
An official with Unintimidated PAC confirmed to the Journal Sentinel that it will begin airing ads Sept. 8 in Iowa. The $6.8 million in ads will be broadcast in Des Moines, Ames, Cedar Rapids, Waterloo, Iowa City and Dubuque.
The PAC also is planning TV advertising in New Hampshire, South Carolina and Nevada, which hold the second, third and fourth primaries.