Citizenship wasn't even a concept in the constitution until the 14th Amendment in 1866! When the constitution and First Amendment was written, it applied to all residents of the US and citizenship was mostly defined at the state level.
> No Person shall be a Representative who shall not have attained to the Age of twenty five Years, and been seven Years a Citizen of the United States, and who shall not, when elected, be an Inhabitant of that State in which he shall be chosen.
> No Person except a natural born Citizen, or a Citizen of the United States, at the time of the Adoption of this Constitution, shall be eligible to the Office of President; neither shall any Person be eligible to that Office who shall not have attained to the Age of thirty five Years, and been fourteen Years a Resident within the United States.
It uses the term of "citizen" but does not specify a requirement or legal definition. The constitution implies a continuance of English Common Law in regards to citizenship:
In regards to slaves or Native Americans - again it depended on the states' laws. Hence the entire reason why the 14th Amendment was passed.
The fact that they only called out the requirement of citizenship for office should make it pretty clear they intended the rest of the constitution was universal.
Maybe it includes a reference to citizenship but it does not define it as a constitutional concept. It also certainly doesn't make it a requirement of the constitution, as sitting US politicians or the OP are currently arguing.
If this is what you are defending than we couldn't disagree more.
It doesn't define a lot of things; treason's the only crime defined, for example, but we knew a whole bunch of others existed on day one.
It does clearly imply a difference between "natural-born" citizens and naturalized ones, and that citizens and residents/people/persons aren't the exact same thing.
The choice to use "citizen" in some spots and "person" in many others seems very deliberate.
