I've seen that tired slogan many times during the past 4 decades or so. We are all immigrants? Really?? Who is "we"? All of my ancestors are from the Midwest of America, i.e., the "heartland" (I'm talking about dozens of people). In fact, I know zero immigrants. Zero! Years ago, I knew a guy from Sicily. So that was one guy out of many, many people. Where are all these "immigrants"? In Jew Yawk Shitty? Ok, besides there, where? Indeed, America's founders were 99.5% native-born:
http://www.vanguardnewsnetwork.com/2017/02/america-its-a-white-nation/

https://dailygazette.com/sites/default/files/adirondack%20creamery%204%20cropley.JPG

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