It's not obvious. There are two methods they could attack. Force cars to make drive dangerously, which is a clear attack on civilians. Or halt all cars, which wouldn't be but would require incredibly dumb design choices in the cars. I assumed the first, and I guess you picture the second.
Your first option is way more devious than anything I had imagined, that's true, but I'm not convinced it would warrant toe to toe nuclear combat with the Ruskies, to quote Dr. Strangelove (or rather Major Kong in that movie). I'd expect something along the line of strict economic embargo, with all sorts of shady people making a lucrative business out of it.
> particularly as an attack on self driving cars would be an intentional targeting of civilians
Except it obviously isn't an attack on civilians.