According to the people we have spoken to, it's reasonably possible that judgments for GDPR fines can be domesticated in the US. Once domesticated, they carry the same force and effect as a judgment issued by a US court. The legal processes for this generally already exist, although there are no GDPR-specific treaties, and it isn't guaranteed that this would occur for GDPR fines - it would be up to the US court system. Like many other aspects of GDPR, it is uncertain at this time. However, I don't want to be the first test case.