It equates trying to achieve a slightly less crushing neoliberal policy (going "left") with literal 9/11. Like, the most lukewarm socdem policies are as damaging as blowing up the twin towers. And it makes no attempts at justifying this comparison; the comic just makes the comparison and expects it to be taken at face value. It's so juvenile that it got a laugh out of me.

It's one step away from saying "you're a doodoo head if you like your guy; my guy is way better and cool ;)"