Why is a background records check (Security Threat Assessment) now required before getting a hazardous materials endorsement (HME)?

The requirement is a result of the U.S. PATRIOT Act (Public Law 107-56, Section 1012), the Safe Explosives Act (Public Law 107-296, Section 1121-1123), ARS § 28-3103(A)(2) and 49 CFR 1572.