From the Heritage Foundation, a conservative institution, discussing the problem with nationalism. It's a thought-provoking piece.
https://www.heritage.org/conservatism/commentary/the-problem-nationalism
Nationalism is great. Should be more of it.
In America, American culture should be king...whatever America chooses it to be.
Closed borders, no massive immigration, etc.
America first, second, and third.
That article links immigration with American exceptionalism and nationalism.
And on that point, I'd agree. What makes America special is that anybody can be an American. That America is composed of people from all over the world, so America has more claim to be global and universal than other cultures. That plus democracy and freedom make America a special country. However it's also very different than the experience in almost every other country. And immigration in the US has always provoked backlashes from white supremacist types in the US.
My election ballot from NJ came with a page of instructions in English, another in Spanish, and a 3rd in an Indian writing system which I've been calling Hindi but that might be an incorrect designation.
Nationalism meaning national pride (in your language, culture, food, land, etc) can be positive. Nationalism in the form of chauvinistic we are better than others, other culture/people are lesser can be a very dangerous thing. Certainly was behind the murderous conquest of colonialism and America's many wars. We're superior, we know best, we'll uplift these poor blighters (as we steal their land/wealth/dignity).