Is Pope Leo eligible to be voted President of the United States?
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No Title of Nobility shall be granted by the United States: And no Person holding any Office of Profit or Trust under them, shall, without the Consent of the Congress, accept of any present, Emolument, Office, or Title, of any kind whatever, from any King, Prince, or foreign State.
But also the emolument clause is effectively unenforceable and the whole "insurgent" ruling basically made it impossible to challenge a presidential candidate. If Trump wants a 3rd term, for instance, I'm not sure what mechanism would prevent him at this point.