There are two principles in diplomatic protection in dual nationality cases.
1st public IL, is based on the sovereignty equality of states and bars protection in behalf of those who are simultaneously also nationals of the defendant state.
2nd its origin in private IL, court of a 3rd state had to resolve a conflict of nationality law, the principle of effective nationality was created with relation to the individual. No irreconcilable opposition between the two principles exists, they complement each other reciprocally.
The state of dominant nationality with which the individual has stronger links may bring a claim against the state of subordinate nationality
The claimant can not be regarded as a US national