Republican megadonor Ken Griffin said at a private conference Wednesday that he'd support Secretary of State Marco Rubio over Vice President JD Vance in a 2028 GOP presidential primary, Axios has learned.

Why it matters: Griffin is one of the most prolific donors in the Republican Party — he gave more than $100 million in 2024 — and would be a huge asset to Rubio if the secretary of state were to run for president.

• Griffin's comments reflected the emerging split in the GOP between establishment-minded figures like Griffin, who want Rubio to run, and anti-establishment types who prefer Vance — in part because of the VP's reluctance to involve the U.S. in foreign conflicts.

Behind the scenes: Griffin was interviewed at the exclusive Allen & Company conference in Sun Valley, Idaho — known as "Billionaire Summer Camp" — by New York Times financial columnist Andrew Ross Sorkin.

At one point during the Q&A, Sorkin asked Griffin whether he'd support Rubio or Vance in a 2028 GOP primary matchup between the two.

• Griffin noted that he'd historically backed Rubio — he donated to him during his unsuccessful 2016 presidential run — and would be predisposed to backing him again.
• The interaction was brief and Griffin, the fifth-biggest donor in the 2024 cycle, specify what he would to to help Rubio.

Yes, but: Rubio has said he would defer to Vance should the vice president run in 2028, as Vance is widely is expected to do.

The backstory: Griffin, a billionaire investor, has criticized President Trump in the past, including in 2022, when he called for the GOP to move on from Trump and said it was "time to move on to the next generation."

• Griffin supported former U.N. Ambassador Nikki Haley (R) over Trump in the 2024 GOP primary. He did not donate to Trump during the cycle.
• Griffin has praised and criticized Trump's policies during his second term. He was critical of the president's tariffs, but has supported his deregulation efforts. Last November, he attended a White House dinner with other Wall Street executives.

The intrigue: During Trump's 2024 VP search, Griffin pressed Trump to not select Vance, I reported in my book, "Revenge: The Inside Story of Trump's Return to Power."

What they're saying: A Griffin spokesperson declined to comment.