What's the American National party all about?
Far-right. Fascist is probably too strong (and clicheed) a term, but definitely far-right. It was a response to the clearly more unstable situation in the US in TTL, and more specifically gained its strength during the worst part of the Great Depression, which apparently happened in TTL almost at the same time as in OTL.
I see them as anti-immigrant and anti-socialist first and foremost, together with standard far-right fare like in favor of curtailing free speech and all that. Probably no religious element necessarily, since in the 1920s-30s American evangelicalism was only beginning to politicize, and then only on issues like evolution in schools, not a general party platform kind of thing.