It is a setup so he does not run again..
There may be more to this than that I fear.
Recall that Garland appointed one Jack Smith as special prosecutor into the Trump document case. He is a bitter partisan, a globalist and a ruthless inquisitor. Smith will conduct his investigation from Washington and will use Washington courtrooms to indict and convict Trump. There is no court in that town in which Smith can possibly fail. Once he draws up his indictment Trump’s conviction and ruin is a dead certainty.
At this point Joe is a liability and an embarrassment. He was probably ratted out and he’s now facing this alone. They’ll let him go down and then congratulate themselves for their fine leadership in reestablishing trust with the American people. Then they’ll cite this unpleasantness to make their prosecution of Trump into a moral crusade and reinforce Smith’s offensive.
Trump’s future is contingent on how this plays out. The chess pieces are lined up.