They were successful at creating fear and making conflict avoidant people stay home. Despite large amount of protesters, that is real effect.
And it would create real vote suppression. You would had people not voting out of fear. And the opposing side having less votes (even if they win, they win less)
Equally importantly, this is not an operation that could be planned in secret or at the drop of the hat. If the Trump regime tries to do something like this, we'll know weeks or months in advance, and there will be plenty of time to make it clear that anyone who participates will face swift and severe justice.