The FBI didnt’ check your birthing records. They just wanted to know if you were a good boy and could be trusted.
I found this article on security clearances.
“Meanwhile, members of congress are not subject to any type of background check. They are merely asked to promise not to reveal any of the nation’s secrets. That’s it. According to a seasoned professional, Winslow Wheeler, with 31 years experience on Capitol Hill, members of Congress are granted security clearance simply by being elected. Winslow worked for the Senate Budget Committee for six years as a security official. He recently published a book about Congress and national security.”