(He is indeed required to assist, as pointed out upthread.)

The DoJ has personnel to make the arrest if he does not turn himself in, which I think he will. Trump wants no perp walk for the cameras.

DeSantis' statement is meant to shore up his standing with Trump's base, which he will need. DeSantis could be the last man standing and benefit politically, but then again, Trump could run from prison and win as a martyr.

I think that last scenario is unlikely — people will give up on a prisoner for president — but I've learned to never say never with this guy.

simultaneously a member of the executive and legislative branches, and neither, whenever subpoenaed.