“State’s right to do what?”
The right of state’s to determine what size mud flaps to require on large trucks. Start with that.
Well when you launch an armed rebellion over mudflaps then we can talk.
So far as I've been able to figure out, there are currently no federal regulation concerning the size mud flaps.
There was talk of imposing such regulations in the Nineties, but apparently it didn't go through.
States decide those regulations.
So all that secession and civil war were unnecessary.
* sigh *