Impersonation on nostr…. The npub (public key) is the thing that cannot be impersonated. Names and other content can be duplicated, but you have to have the associated private key to sign for a given public key. So Biden would have to have a known public key associated with him.
You’re right that there is still a problem here because even if we had an npub associated with Biden’s presence on a platform like nostr we know that he probably doesn’t even run his own Twitter account. There has to be some incentive to know that the person doing the signing is actually the person associated with the public key. The only way we are going to get there as a society is if people start actually using their public key as an identity to the point that if they give up their key then they are giving away their identity. It would be logical to use a system like this instead of social security numbers, but there obviously isn’t a system in place that would have meaningfully allowed Biden to prove anything today. People complaining are being idealistic