I’m gonna ignore the political stuff and actually answer your question: impersonation is a shit thing to do no matter who the target is, but there’s no centralized authority or terms of service in the fediverse. That’s kinda the whole point of it.
The above user is on mastodon, so they can verify their identity there by adding a line of code to their web site and then linking to their web site on masto. Instructions here: barrd.dev/…/add-a-verified-website-to-your-mastod…
Once they’ve done that, they can pin a toot saying only to trust this account and no others.
If they don’t have a web site, welp. Never too late to make one.