[US] Assuming Trump really can end birthright citizenship with an executive order, would citizenship be revoked for people who were born prior to the order?

I know that a lot of legal scholars are saying that Trump can’t end birthright citizenship by executive order. But a lot of lawyers are also saying that it’s completely within his power.

My question is, what happens to the people who are currently considered citizens if Trump ends birthright citizenship? Are they immediately not citizens? Or do they get grandfathered?

If they don’t get grandfathered, What happens if that creates a cascading chain of non-citizenship through multiple generations? What happens if you have people who can’t definitively prove their citizenship across 100+ years?

Won’t this affect a lot of people? My understanding is that a lot of people used birthright citizenship to establish their citizenship in the WWI - WWII era. How will anybody know who a “real” citizen is?