I've had comments voted lower than -3 (you start at 1) plenty of times. My favorite one is one comment criticizing Microsoft that oscillated from 25 to -10 a few years back (yeah, I refreshed this one quite a lot to see how it changed, that was fun).
But I don't remember anything lower than that recently, so it can be a new change.
I can downvote but rarely do it. Also a comment can only be downvoted 4 times. After that downvotes are not counted anymore if I remember correctly.