In general trolls can get away with a lot, although here on Medium they do actually enforce their content rules, which includes the following.

Harassment
Medium exists to share and discuss ideas. We don’t tolerate harassment, which includes:

• Bullying, threatening, or shaming someone, or posting things likely to encourage others to do so
• Using Medium features like responses, private notes, mentions, follows, story requests, or writer requests in a way intended to annoy or harass someone

The “…” is at the bottom of every story and comment box, just waiting to be selected to report content that violates Medium rules and when appropriate, I use it.