"But Vox did seem to be saying that most White Americans would more likely than not identify with a single national-ethnic identity rather than the broader racial identity White"
That's the sort of nonsense that I've spent years refuting over and over again, apparently to no avail.
There are solid reasons for differences in the "success" (*) of ethnoracial nationalism between the USA and Europe, other than the majestic "superiority" of narrow ethnonationalism. These include but are not limited to:
1. The greater professionalism and competence of leadership and membership cadres in Europe.
2. Within Europe itself, continental Europe has always had more developed nationalist parties and movements than the UK, for reasons which are likely deeply rooted in cultural and historical phenomena. The overseas anglosphere, including the USA, have seemed to inherit the more muted propensity for nationalism of the UK.
3. As discussed by Le Brun in a podcast, social pricing is much weaker in Europe than in the USA. Yes, Europe has "hate speech laws" but I believe that social pricing is a far more potent force in stifling dissent. Even with factor #2, if you relieved social pricing in the USA, racial nationalism would flourish. But defeating social pricing would require real leadership (see #1).
4. In America, social pricing is strictly reserved for White racial activism, which is what the System fears. You want to organize an Irish-American, German-American, Italian-American, etc, club at your school or place of business? No problem! Looked on benignly. Organize a European-American club? Oy vey, the racism! Then Day's SJW's would really come out. Don't you think people know this? Don't you think we need to break that barrier to have success?
*I put "success" in scare quotes because people are grossly overestimating the power of ethnonationalism in Europe where an outright invasion by young NEC and African males is being greeted with the enthusiasm of a sex starved female virgin getting screwed by a lustful alpha male.