KASKY: Senator Rubio, it's hard to look at you and not look down a barrel of an AR-15 and not look at Nicholas Cruz, but the point is you're here and there some people who are not.
This video is about the town hall meeting held after the Florida School shooting. And I don't know what "look down" means here, so I'm having a difficulty understanding a whole sentence. I looked up the definition of "look down on" which means to think that you are better than someone, but I think it definitely doesn't fit this context.
What's the meaning of the sentence?
For those who don't know, Nicholas Cruz is the criminal and AR-15 is a gun he used.