Trump may see Jeb as weak.
Trump is a bully.
Bullies love to pick on people they perceive as weak.
It’s just kinda fun for them.
(another possible explanation)
He attacks anyone who is even remotely “mean” to him. There is no plan.
Appears to lack basic self control.
You’re right, but it’s peculiar that Trump’s psychology has not changed at age 69. I’ve met a lot of ex-bullies in their 20’s.
You wish.