Drug cartels do mass shootings all the time, just not here in the States. Aside from a targeted hit here and a kidnapping there, cartel leadership is very disciplined about keeping the worst of their violence on their side of the border. They want it that way. Less involvement from us if it is a Mexican problem.
There’s always a ‘first’. 0dunga has opened our border like never before. Syrians are pouring in, even.
And now there is no border, so, Ta-Da! (allegedly on the perps)