I mean, the easiest starting step would be: Identity Verification via the methods Discord switched to after realizing Persona was horrible.

Much more ideally, some sort of government-ran zero-proof service where Anthropic can confirm solely that you are a valid US Citizen without Anthropic gaining enough PII to link my account to a particular legal identity (these already exist)

Of course, if your adversary can't just buy a dozen US Citizens, they're not really much of a threat to begin with... (there are lots of ways to buy people: explicit bribes, people of questionable loyalty, scam them, or just hack into a dormant account with an annual subscription)