The famously dangerous threats that are thoroughly documented college level students. Americans have commited the majority of terrorist attacks in their own country, especially if you count school shootings
Not sure how we pivoted to "terror" from "national security," which is much broader, but since we are here:
School shootings are not typically classified as "terrorism" unless they are explicitly motivated by political, ideological or religious agendas.
Foreign-sponsored terrorist attacks, such as 9/11, San Bernardino shooting, Pulse nightclub shooting, etc result in significantly higher casualties, widespread fear and greater economic impact (in the $trillions). Foreign actors are typically more sophisticated, thus calling for enhanced screening. And their actions have further-reaching consequences such as the cost of wars and homeland security measures.
School shootings are not typically classified as "terrorism" because they're overwhelmingly done by white males. The same reason the current administration refuses to react to white nationalist terrorism.
