U.S. President Donald Trump speaks, as he and Apple CEO Tim Cook

Trump megadonor and billionaire hedge fund manager Ken Griffin isn't afraid to criticize President Donald Trump or those who enable him.

In a Wall Street Journal (WSJ) opinion piece published Sunday, the founder/CEO of investment behemoth Citadel criticized Trump's attacks on the Federal Reserve and challenged the credibility of economic data used by the administration to justify the firing of the head of the Bureau of Labor Statistics. And the Murdoch-owned WSJ did a deep dive Monday into Griffin's resistance to Trump, calling him "the most outspoken critique from a business leader in Trump’s second term." The outlet noted that "other prominent executives haven’t seen upside in going against a president who singles out people or companies for retribution over alleged slights."

In his Sunday op-ed, which Griffin co-authored with University of Chicago professor Anil Kashyap, the Republican donor wrote that Trump's actions "raise inflation expectations, increase market risk premiums and weaken investor confidence in U.S. institutions."

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Griffin also defended the targets of Trump's attacks, with the Journal reporting that the wealthy investor "came to the defense of Walmart CEO Doug McMillon after Trump attacked him for raising prices in response to higher tariff costs."

"Shame on the administration for criticizing an American CEO, who has done an extraordinary job of helping to have people get more for their dollar, more for the hours they work, for just being honest,” said Griffin, who once called Trump a "three-time loser" at a June conference.

The Citadel billionaire donated over $100 million to conservative candidates — a third of what Tesla and SpaceX CEO Elon Musk gave — in the 2024 election cycle, but never directly contributed to Trump, saying he voted for him, but "not with a smile on my face," eventually plunking down $1 million to Trump's inaugural committee. It remains unclear whether Trump will set his sights on Griffin, given his reputation as a reliable donor to his party's candidates for Congress.

"Trump has reason to be diplomatic in his approach with Griffin as the GOP looks to the midterm elections," the WSJ said.

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Click here to read the WSJ's report in full (subscription required).