What’s failing, exactly? I wonder if, like intel agencies pre-9/11, mass shooting threats are lumped in to a vastly broader pool, responsibility spread across many agencies federal and local, so no single force is in charge, dedicated to spotting them. Dedicated local task forces like the ones described here strike me as having a great deal of potential. We should be thinking and talking about them more.
There is, to my knowledge, no dedicated national law enforcement + criminologist group specifically looking for potential infamy shooters, for institutional holes that might impede finding them, or trying to educate local officials on warning signs. This may also offer a way to think more clearly about security reforms and the like — Not arming teachers or lightly trained, bored rent-a-cops, but increasing both random and occasionally intel-based patrols by trained police who are specifically there to deter shooters.