- never signed up for anything like this,
- never donated to or signed up for emails from the DNC, et al.,
- political texts like this come all the time, and
- I hesitate to reply “stop” because I don’t want them to know this is a live number (is my instinct here outdated/inapplicable?)
Your instinct is wrong. If you want them to stop, you have to tell them to stop.
Yes, they will add you to other phone lists, but I think they’ll do that whether you text STOP or not. Also, it takes like 5 seconds.