There were several warnings to the FBI about this guy... could it be they were to distracted trying to bring down a president to take action?
https://www.buzzfeed.com/briannasacks/the-fbi-was-warned-about-a-school-shooting-threat-from?utm_term=.uxbRkBPNE#.ueEa05LqE
Yep, the FBI is too focused on being anti-Trump and CYA to actually serve the public.