Donald Trump's Grandpa was a German immigrant

I don't get where you are going with this.

A lot of people that come to US are immigrants. The forefathers were immigrants.

Also considering if the descendants were born on American soil, then that already legalizes them as American civilians. That is assuming if not already nationalize otherwise after coming to the country.

So? What’s your point. Biden’s ancestors the Robinette’s owned slaves.

If Friedrich Trumpf hadn't changed the spelling of his surname after settling in America, then the 45th President would have been "Donald J. Trumpf" ;)