Legitimacy is given by the people
Right, and you know who ratified the Constitution? The People. If the authority isn't specifically listed in the Constitution, the people have not consented, and the authority is not legitimate.
I see an eerie resemblance between this argument and that of morality/ethics with Fundamentalist Evangelical Christians....
We're beginning to have a schism between fundamentalist constitutionalists and catholic (lower-"c") traditionalists in the US....
Thank you. That is exactly the question of legitimacy.
In pre-modern times, be it monarchy or theocracy, the source of legitimacy was god. Directly. The kind if the appointed representative of god.
In modern times, we have republics, where the people are the legitimate source of the constituent power (the power that CREATES the constitution). But we also have theocratic and quasi-theocratic states, where there is a power behind that, so the bible is the source of the constituent power.
And here is the interesting part of a quasi-theocratic state (which some are trying to turn the USA into): the true constituent power has no limits or bounds except international treaties regarding human rights. That it. If the constituent power is bound by the bible or religion, it is not a true source of legitimacy, that moves back in the chain and is now no longer the people, but the bible/god/whatever.
When that happens, you pretty much destroyed the whole idea of a republic, and turns back into a quasi-theocracy, or a theocracy disguised as if it were a republic. Really, really bad idea.