>> reporter: the mental illness argument is a convenient retreat, but it's not like other countries are free from mental illness or violent video games or disaffected youth or any of the other proxies we blame after every new mass shooting. it's only in america where the combination of a young man and a loaded gun have led to so many tragedies, so many dead. >> just another day in the united states of america. >> reporter: when there's an attack by an islamic extremist, we have no problem calling that terrorism. the american war on terror has identified a very specific enemy. in this case, the shooter in el paso was on a different kind of terrorist mission. this was homegrown domestic terrorism. the targeted murder of immigrants and latinos, to try to spread the ideology and the aims of white nationalism. >> this is disgusting, intolerable. it is not texan. >> reporter: white nationalism is an american terrorist movement as old as the klan, as