That isn't uniquely a feature of whiteness exclusively, though white people by and large are beneficiaries. What is different about white people, or at least the nation-states founded by our forebears, is that there is a vision for someone who is non-white to become a citizen, to become a countryman.
You could become German. You could become French. You could become British. You have become American.
It is highly unlikely I could become an Indonesian if I weren't married to WNI. It's even more unlikely I could become Japanese or South Korean, or Chinese.
White people are chided for resistance to immigration when we're largely the only people who advocate for it. I don't blame developed economies, save Singapore, in Asia that are reluctant to share in the wealth of diversity. It's a pain, it's a real burden to shoulder that ever growing lack of cohesion. They can easily point to the crises facing the United States, Canada, EU, and Australia as all the more reason to be cautious of calls to diversify their populace.
MAGA is indeed as you say it is. Its adherents seek a return to whiteness as the default identity of the United States. What is to be its successor identity? With the rise of apparent monocultures outside of white-majority nations, how will we differentiate ourselves?
Sure, USA and Western Europe tend to have a more progressive stance on immigration, but it is heavily challenged today, and you can forget Eastern Europe.
Indonesia was not free until 75 years ago, there are still Indonesians alive today who experienced life as a Dutch subject, including my dad. The experience of being occupied by a foreign power is still too recent for people to accept a progressive attitude toward immigration. You really can’t discuss this fully without considering the legacy of western colonialism and imperialism.
In the case of America, the entire population except the natives are immigrants or their descendants. A German has a stronger case to resist immigration because his ancestors have lived there since prehistoric times, but an American really has no moral ground to oppose immigration in principle. The only limitation is practicality.
Speaking of cohesion, immigrants from France, Spain, Germany, Ireland, and Italy come with their own language and culture that don’t exactly match WASP tradition. Somehow these folks meld together into the modern concept of ‘white’ in USA. It’s a little rich to then claim that this mongrel culture needs to be protected from dilution.
The question about “who is an American” is a complicated one when you look from the inside, but somehow easier for an outsider to answer. Ask the Brits, French, Australians, and Indonesians here about what makes one an American, and you’ll find better answers than simply ‘whiteness’.
As somebody who is both an outsider and an insider, I have a certain perspective on the subject.
One of the definitive traits of an American is his/her belief that anybody can become an American. Not just a “citizen of the United States of America”, but an actual American. Being anti immigrant is so socially unacceptable that Americans (except for straight KKK members) who harbor the sentiment always soften it up by saying they’re only against illegal immigration. Then they elect politicians who promise or imply limited immigration.
An American has a distinctive and unique concept about the importance of certain freedoms, but in combination with a strong desire for law and order.
There are many other things to mention, but what I’m trying to say is that being an American is so much more than being white.
Here’s a tangentially related video from Trevor Noah. Please don’t take this as a dig to the French, it’s just comedy.