[thyristan]

> We the People of the United States [, in Order to ...,] do ordain and establish this Constitution for the United States of America.

That is the literal first paragraph of the US constitution. I cannot imagine a valid legalistic argument that ignores that. When first establishing the constitution, it also didn't appear in a vacuum, the pre-existing states and confederation were already democratic for some time. So all authority/validity/legitimacy the US constitution has comes from the population, back then. And through continuing use, participation and broad acceptance until present.

And of course, as a practical matter in a representative democracy, between elections, the people do have far less of an influence. They can basically only voice their opinions, threaten to vote differently in the next election, or start a revolution. But that doesn't absolve them of their responsibility on election day.

[vintermann]

> So all authority/validity/legitimacy the US constitution has comes from the population, back then

Exactly, back then. But those people are dead to a man. They are no longer people of the United States. Even if you count them as such, they would be extremely outnumbered by currently living people of the United States, and thus, democratically they can no longer confer any legitimate authority to the constitution. If they do confer any authority, it isn't democratic authority, because it has to be based on something else than the people.

> And through continuing use, participation and broad acceptance until present.

I think that's a pretty tenuous argument, all the time people constantly point to the constitution itself as authority for why they accept the constitution, rather than pointing to themselves as they should if they truly believed in the people's authority as opposed to gods, kings and holy texts. But even accepting that argument, at the very least you'd have to agree that if the people decided to change the constitution through means other than those the constitution propose, then that could still be perfectly democratic.

[thyristan]

> But even accepting that argument, at the very least you'd have to agree that if the people decided to change the constitution through means other than those the constitution propose, then that could still be perfectly democratic.

Yes, of course. If the voters, or at least their democratically elected representatives, decide that a new and different constitution is necessary, that's totally fine and expected. Some more modern constitutions even point this out explicitly.