I have a question about handshake etiquette

[Bernie Sanders Endorsed Graham Platner - We Joined Forces & Confronted Susan Collins - Vermont & Maine Alliance To Crush Fascism & Oligarchy - We Didn't Hold Back : r/vermont](https://www.reddit.com/r/vermont/comments/1n4spyr/bernie_sanders_endorsed_graham_platner_we_joined/)

It has to do with the post I linked, the man in the beginning takes Susan Collins hand and holds on to it to keep her from walking away.

there is a comment about how this was "disturbing" and undermines the message. I feel like there are different rules for politicians (especially ones with a track record of avoiding talking with constituents)

So what DOES etiquette say about taking someone's hand for a shake and not letting go?