How are US candidates for political office qualifications vetted?

Putting aside the specific question/s about the current President’s citizenship status and qualifications for the office he holds, how are candidates for all federal electoral positions vetted? How do we know that we are nominating / contributing to / campaigning for / voting for / installing into office candidates who meet the minimum Constitutional and statutory qualifications for the office? Who checks this stuff?

Aside from the fact that “voters” as a class aren’t qualified to do this type of checking (if the President himself hand-delivered his birth certificate to me I am unqualified to verify whether it’s real, unaltered and actually his own, for example, or even to investigate further), “media outlets” aren’t part of the government and could have their own biases, just like party leaders, and it doesn’t make sense to have 50 state electoral boards come up with 50 different ways to check federal candidates. (And how do they check / certify candidates for State offices?)

And just to repeat what I’ve said on the topic in other threads: though I don’t support many of this President’s policies, I fully agree with his attitude that “I have nothing to prove” in this regard. Without a Constitutional requirement that his qualifications be checked, we pretty much have to take him at his word. Same as with every other office holder.