• Citadel Securities ripped Trump Media CEO Devin Nunes for a letter he sent to the Nasdaq that mentioned Citadel Securities and other major market companies after warning of possible illegal short selling of Trump Media shares.
• "Devin Nunes is the proverbial loser who tries to blame 'naked short selling' for his falling stock price," a spokesperson for Citadel Securities said of the former Republican congressman.
• Citadel Securities' founder and non-executive chairman is Ken Griffin, who has been a major donor to GOP candidates.
• Donald Trump, the presumptive Republican presidential nominee, is the largest shareholder in Trump Media.

Citadel Securities ripped Trump Media CEO Devin Nunes on Friday for a letter he sent to the Nasdaq that mentioned Citadel Securities and other major market companies after warning of possible illegal short selling of Trump Media shares.

"Devin Nunes is the proverbial loser who tries to blame 'naked short selling' for his falling stock price," said a spokesperson for Citadel Securities, underscoring the sharp fall of Trump Media stock since it began public trading with the DJT ticker in late March.

Citadel Securities' founder and non-executive chairman, Ken Griffin, is a major donor to Republican candidates — among them Nunes, a former GOP congressman whose company owns the Trump Social app.

"Nunes is exactly the type of person Donald Trump would have fired on [The] Apprentice," said Citadel Securities spokesperson, referring to the former Republican president's business competition reality TV show.

"If he [Nunes] worked for Citadel Securities, we would fire him, as ability and integrity are at the center of everything we do," the spokesperson added.

A Trump Media spokeswoman fired back, saying: "Citadel Securities, a corporate behemoth that has been fined and censured for an incredibly wide range of offenses including issues related to naked short selling, and is world famous for screwing over everyday retail investors at the behest of other corporations, is the last company on earth that should lecture anyone on 'integrity.'"

In a filing later Friday with the Securities and Exchange Commission, Trump Media noted it issued that response on its Truth Social and to media outlets.

"Rather than support our common sense efforts to promote transparency and compliance, Citadel Securities bizarrely targeted our CEO with an unhinged attack," the company said in that filing.

Nunes' letter to Nasdaq CEO Adena Friedman was dated Thursday, the same day that Trump Media notified the SEC it had issued shareholders detailed instructions on how to avoid their DJT shares being used by short sellers who are betting that the price of the stock will fall.

While Trump Media's share price has risen strongly in the past three days, it is still trading sharply lower than its debut opening price on March 26.

The company, which owns Truth Social and had just $4.1 million in revenue last year, has seen its market capitalization shed billions of dollars as a result of the share price drop.

Nunes told Friedman in his letter, "I write to bring your attention to potential market manipulation of the stock of Trump Media & Technology Group Corp."

Nunes suggested that Trump Media's price had been used for so-called naked short selling, a practice in which traders sell shares of a company that the seller had not actually borrowed for that purpose.

Nunes said brokers had a "significant financial incentive to lend non-existent shares" to short sellers because of the unusually high premiums they have been able to charge for such loans of Trump Media shares.

"Data made available to us indicate that just four market participants have been responsible for over 60% of the extraordinary volume of DJT shares traded: Citadel Securities, VIRTU Americas, G1 Execution Services, and Jane Street Capital," Nunes wrote.

Citadel Securities has been the only one of those four companies to comment on Nunes' letter.

The strong language in its response is striking, particularly because of the political background of people involved in Trump Media and Citadel Securities.

Nunes resigned his seat representing a California district in the House of Representatives in late 2021 to become the head of Trump Media when it was privately held. The company became publicly traded last month as a result of a merger with a shell company.

Donald Trump, who is the presumptive Republican presidential nominee, is the majority shareholder in Trump Media, holding a stake of nearly 60%.

Citadel Securities' founder, Griffin, contributed $5 million to a political action committee backing former South Carolina Gov. Nikki Haley in her unsuccessful campaign against Trump for the GOP nomination.

In September 2021, Griffin donated $5,800 to Nunes' congressional campaign, three months before Nunes said he was resigning his seat to become Trump Media's CEO, according to a Federal Election Commission filing.

Citadel Advisors, an investment management firm also founded by Griffin, as of December owned nearly 160,000 shares valued at $2.8 million in Digital World Acquisition Corp., the shell company whose merger with Trump Media last month enabled Trump Media to become publicly traded.

A Citadel spokesperson told CNBC, when asked about that stake in DWAC, said, "Consistent with our role as a market maker we often have some level of inventory for highly traded shares."

"The purpose is to facilitate trading for clients, not to take a directional bet one way or another," the spokesperson said.

— Additional reporting by CNBC's Brian Schwartz.