A GOP megadonor revealed at a private conference on Wednesday that he intends to back Secretary of State Marco Rubio over Vice President JD Vance should the two men decide to run for president in 2028, according to a new report. Axios reported that Ken Griffin, CEO of Citadel LLC, said during an interview at the Allen & Company conference in Sun Valley, Idaho, that he would be "predisposed" to backing Rubio because he previously backed his faile…