Secret Service agents fatally shot 21-year-old Nasire Best after he opened fire at a White House security checkpoint while the president was inside.The assailant, who had a history of psychiatric issues and previous arrests for trespassing, wounded one bystander before being neutralized.This incident follows a series of recent security challenges including an attempt by another individual to breach a major media event.Federal agencies are continuing to investigate the motives behind the shooting as they address a rising trend of political violence across the nation.