[Edit - My first joke was nonsense! Trump isn't president now! It made perfect sense in my head though. Haha.]
Fixed joke
He says Junior is VP. Trump wins. Trump gets inaugurated. That night Junior cries because Trump uses his "official act" powers to immediately put in Barron as his replacement.
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Sure he could be. Trump comes out to the media and says "Barron's not 35. But it doesn't matter. I said to myself..." He points to his own head "Self - the VP age is whatever Trump wants it to be. So - official act. Done. Barron VP."
"President Trump - what happens if the Supreme Court disagrees."
"Disagrees? Bad justices are not loyal so they are done. I get new justices to replace them."
"Done? What does 'done' mean?"
"Things end. People die. It's sad but it happens. Can be quick."