doomer

Is there something intrinsic to the calvinist branches these people follow that instills bigotry?

I really think it's the material conditions of descendants of white settlers having an economically advantageous position over people of color and immigrants that leads them to being more disproportionately petite bourgeois than those demographics and deeply fearful of encroaching proletarianization as a result, and that economic relation driving cultural superstructure phenomena that reinforce and solidify those bigotries.

Anecdotally, my grandpa sounds pretty similar to your dad in ways. He was a WW2 vet that was on Omaha Beach that lied about his age to enlist young because his family was broke after the Depression and Dust Bowl in the Midwest and wanted to get out, fucking hated Nazis and anything resembling capital-F Fascists his entire life, fell in love and married a Japanese woman and started a family with her after being stationed there after the war and then fighting in Korea and getting honorably discharged after getting a purple heart in service, went home and settled down in Kansas after he got out, but still was a zealous anti-communist cold warrior and soft racist despite having biracial children and being "a good democrat."

My aunt told me a story of them eating dinner with him once at his house when they had the TV on, and the local news had some story about a local Klan march that had a scuffle with protesters and cops, and when the Klansman was interviewed about it, grandpa said something like "well I don't like them but he's making some good points about the races all being better when they're with their own kind," and my aunt was just like "what the fuck dad, mom's Japanese and me and my siblings are mixed race and you always say we're the love of your life" and he was just kind of dumbfounded for awhile. He was personally a really sweet person and the kind of old lib that liked to talk up any opportunity to describe a person of color he interacted with at a job or something as "what a nice guy" and "really professional" as a way of showing his "not-racist-but" bonafides but betrayed a lot of his own prejudices unknowingly in doing so. There were and still are a lot of those kind of people in America.

That's a big factor, but the Anglos and German immigrants played a big part historically, and it shifted eventually to eastern-European immigrant groups and Latinos as the moving target of "American" shifted from the late 19th century to the post-WW2 era to the current day. I'm far from an expert on it, but from what I know, a similar thing has kind of happened on the right in Brazil in Bolsonaro's base of ex-Catholics becoming born-again Evangelicals because of their relative comfort and economic security becoming at odds with Francis's more collectivist/soft-left messaging meshing with Lula's platform.