If their bank has dealings in the USA, they can be de-banked. If they use American credit cards, those can be shut down. Accounts for companies based in the USA can be disabled/deleted or otherwise flagged. They can be blocked from flying on American and allied airlines, or from flying through those countries.

Basically the US government will convince whoever they can to stop dealing with that person, or just to fuck with them in any way they can.

Barista

That just means even anonymized it can be traced back to you.