And given the party Daniel supports, saying he doesn't want a monoculture... it seems like you are being naive. There are lots and lots of right-wing people in the USA that over the years never said far right things... but their actions have shown a different story.
I think you need to judge Daniel on his actions, not his words or your gut.
Again, I'm not defending his choice, but no, I'm not being naive. Over the 20 years I've known him he has demonstrated his values through consistent words and actions. I'd share details but that's not my place to do. You may choose to believe me or not.
Your choices are to either end a 20 year friendship and enormously fruitful collaboration or defend someone who has demonstrated quite clearly that he holds repulsive, despicable beliefs.
Imagine you were of immigrant background and your closest friend gave millions of dollars to a party whose sole platform is to strip you of citizenship and kick you out of your country.
I have no idea why people assume immigrants are pro-immigration. They're pro-themselves.