Most states’ laws leave the vetting to the major political parties. Anyone who gets a major party’s endorsement is good to go. Citizens CAN challenge candidates’ names being placed on a ballot. In 2012 there were 50 challenges heard by state elections boards and courts in 22 states plus the District of Columbia. No challenge was successful.
Proof more of a herd mentality than that he is qualified. The Media would bring down much hardship on anyone who dared.
To date, we are simply relying on the word of Nancy Pelosi as the only evidence that he is legally qualified. To my knowledge, no actual proof of his alleged birth in Hawaii has been presented to any controlling election authority.