My little brother joined the Border Patrol many many years ago and he had to undergo an extensive background check and security clearance.
Why would we not expect the same from those running for POTUS? The only answer I could conceive of is that the n power corrupt the clearance process and only clear those who they want to see elected.
But there has to be a way to ascertain the basic requirements???
The President is not subject to a security clearance. By electing someone President, we are giving him the ultimate security clearance. I don't agree that the FBI should get a veto over a candidate because they might fail a background check. Though would subvert our democratic system.