I'm finding STOP works for US politician texts. They unsubscribe me, at least for that particular spam project. (Inevitably I end up in the next one.)

I don't bother responding STOP to the obvious scams. They're already so crooked I doubt they're going to pay attention to SMS niceties when messaging me from Romania about my USPS package.

PS: never ever give your phone number or email address to any political candidate. Mailing address is required in the US but no other contact info.