He's not going to run for POTUS again. Too old, and wouldn't stand a chance against Trump or Desantis anyway.
Probably just wants to distance himself from the current GOP because he knows how history will look at them, plus he knew she was getting confirmed anyway.
this is likely the correct answer..though he is a bit of a carpetbagger and carpetbaggers generally crave power so i wouldnt say its impossible. i envision desantis flopping in a primary too