To have privileged access to any kind of sensitive national security information, people like me need to submit themselves through exhaustive background checks.
Most common reasons for being rejected of a security clearance are: drug use, any affiliation with terrorists, any kind of anti-American sentiment, being a member of the Communist party, and/or foreign ties of any kind.
But here’s the thing about our system. Presidents do not need to get a security clearance. They are automatically provided access to everything because they were elected by We The People.