Nationalism requires a strong sense of identity and unfortunately people don't identify that strongly with their genetic markers. People wrongly assume that that groups like generation identity are cultural nationalists when they are ethnic identitarians. Being ethnically French is being a part of a French community and a larger french family. A Somalian is obviously not going to be a natural part of a French community.

The main problem in the US is that there isn't really a white ethnos. There is no real historical continuity or specific ethnic group. I strongly dislike protestantism, and I am not that enthusiastic about Christianity in general but Christian nationalism is probably the only realistic option in the US. The one sense of community and belonging in many American towns is the church. The churches have in many cases been the focal point of their community for centuries. American towns tend to lack public places but the church is the only real place where the community gathers.

Their church is the closest thing many white americans have to an ethnic group. Many ethnic nationalisms have been religious in nature.