I'm wondering if a monarchy could technically become a State in the US (without switching to republic, obviously), according to US constitution and to US laws.
I.e., for the sake of the question, it doesn't matter if there are no suitable candidates right now. Just about an hypothetical monarchy sitting around over there, wishing to be part of the federation.
Of course it would have to renounce full sovereignty, obey federal laws, like other states do.
Is there anything specifically prohibiting such a thing?
Obviously assuming it would still allow the citizen to vote for a Governor, like other states do, while the Prince would either be a mostly ceremonial title, or it would have some sort of power but within reasonable limits.