I don't get Sullivan's deal

SPOILERS!

The bad US military guys led by Lt. Col. Jack Sullivan. chasing El, shooting up the lab in desert, and trying to take out El with the sniper in the helicopter, succeeding in taking out Brenner.

Those are US military that are taking out FBI guys, cops, murdering all the scientists, shooting up the homes of civies, etc.

How are we supposed to suspend belief that this US agency has the power to perform open warfare like this on US soil against US citizens? In EP 8, Sullivan said something about stopping the killings--is he talking about the 3 kids killed by Vecna back in Hawkins?

I mean, regardless of the fact that the Rooskies are somehow involved, or do they thing that Brenner, Owens, and El and all of that working for the Russians?

I like the show and this season mostly, but this angle seems all too much, like there's no real good motive to have this level of battle operations openly in the US, broad daylight, etc.

EDIT: I admit that my memory of S3 is a bit foggy. I guess the Sullivan character story was started back then (or maybe earlier).

ADDITIONAL THOUGHT: I was just thinking back on the Spielberg era that this show is semi-modeled after and yeah, there's a lot of kids trying to maneuver around the scary big government MIB types that just don't understand. But in those films, did we ever have anything like kids burying FBI guys in the desert?