On second thought, when it says, "No person, etc" in Article II, Section 1, Clause 5, isn't that "law enough," since the Constitution is the supreme law of the land? Understand, I'm not an attorney, but to my naive eye, doesn't "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;" cover it? Like I said, I just assumed someone vetted this. My duh. .
All that has been necessary from the “states” to “meet that requirement” of the US Constitution is for someone to sign a notarized statement to the state (usually the state’s form for candidacy) and say that they meet those requirements.
You do it all the time yourself. You may not have to “prove” to a bank or some agency or “whatever organization” that you meet this qualification or that qualification. They simply ask you to sign it to the effect that you do meet the qualification. If you lie, you’ve committed a crime. But, you signing it saying that it’s true, comes under the penalty of the law if you’re lying, you see.
For example, you sign a statement to the IRS saying that you have no other income other than what you’ve indicated to them on the form. And then that’s all that is required. BUT, if they find out later that you’ve lied - you’re in a heap of trouble.
SO ... it’s not an unusual procedure as people do it all the time in their own everyday lives. They sign statements asserting that “this or that” is true - under the penalty of law.
That’s basically what the candidates have done in the past and what the states have required of them - simply stating under the penalty of law that they meet those requirements of the US Constitution.
The US Constitution doesn’t say that you “have to prove it” - it simply says that you have to “BE” all three of those requirements. The states have taken the “route” that simply does what you’ve done many times over again in signing some “legal affirmation” that is required of you (that you meet some qualification that is required of you).
The PROBLEM comes in only in the case someone has lied. If that’s the case, all that is required to disqualify someone is to provide proof of their lie and then they’re disqualified.
Or, if you want to “PREVENT” a problem from happening in the future, then one can take a pro-active stance on the issue and then require a certified birth certificate from the state that someone was born in - and make that being supplied with the application (for candidacy) a requirement.
It’s a simple thing - just require a certified birth certificate (whatever is required by courts for proof of birth in a state, or whatever is required for getting a drivers license, for instance) - to be submitted along with the notarized signature on the state form.
BUT ... once again ... as far as what has already happened in the past with prior candidates, no state has ever made a certified birth certificate from the state that the person was born in a requirement. They’ve only required a person state that they’re qualified and have the signature notarized. That’s the legal document that the candidate provides. If someone knows that the candidate is lying - then all they have to do is prove the lie.