Rather, where are their true allegiances? It is relatively easy to become a naturalized US citizen, versus say, a citizen of the PRC.

Highly, highly, controversial and politically incorrect tak, but are there people (and entities, including nation-states) that take advantage of that for their own purposes? I wouldn’t doubt it.

I know people who are naturalized US citizens (or even second generation immigrants) from countries friendly and allied to the US, who, if hypothetically asked who they would fight for in a shooting war, would pick their country of origin without hesitation.