YSK the voter protection hotline phone number for your state if you witness any voter intimidation or harassment if you are voting in person.

Who do you call when it's the police doing the harassing?

This is the group handling hotline coordination: https://866ourvote.org/about/

This one is actually administering the English-speaking hotline: https://lawyerscommittee.org/

They don't go into specifics of how they handle things, likely because it will vary by situation, but it sounds like they have a number of tools and actions at their disposal.

Not American, and couldn’t find a non-partisan resource, but here goes:

https://democrats.org/civic-engagement-and-voter-protection/

Our voter hotline exists to answer questions that cannot be easily answered online. The hotline is monitored by DNC employees who are prepared to field questions pertaining to felon disenfranchisement, voter purging, poll worker misconduct, voter machines, and accessibility. The hotline regularly operates on weekdays from 9:00am-6:00pm EST/EDT, and expands to both weekdays and weekends from 9:00am-9:00pm EST/EDT starting in October during election years.