Why?
You're right, Dexter, don't rub their noses in it. No need. Just take the money from a pet boondoggle and spend it where it will do much more good.
I must note an objection, though, to the title. Trump didn't take money from California. He got Federal (our) money back, because California wasn't going to use it for what they said they were going to do.
It was only "California's money" contingent on building the train they can't build.
Return it to the coffers, and if it just so happens it ends up financing part of the wall, well, so much the better.