If the Senate sends him a subpoenas. That is an open question.
A lawyer who calls a witness when it is not certain what he will say is probably a fool. There may be times when you need a hail mary, but this is not that time.
Is it his choice?
Well great job Jon, add ammo to the rats demand that they can call additional witnesses to the BS circus. It was really fizzling to nothing then he volunteers to sing. FU Bolton.