Maybe I don’t understand the US system but I believe platforms are individual to candidates and that there are no overall party platforms that the candidates are expected to adhere to.

Sincerely don’t mean to be rude, but the first 7 words provide the answer. Even when there are no official overall party platforms, the eyebrows waggle in a certain direction. Especially where campaign funding is concerned.

I think this is my point: when do they fight the lesser evil?

I do my part. Many others do too. The fighters are in the minority, which is why it’s so important that the bystanders at least make our work easier.