Given that one of the very few powers that the Founding States delegated to the feds, expressly via the Constitution, to regulate an aspect of intrastate commerce that can affect many citizens on an almost daily basis is the US Mail Service, such power evidenced by the Constitution’s Clause 7 of Section 8 of Article I, the Founding States would likely be confused as to why political parties are now fighting to control the US Mail.
Do you have a theory?