He was born to a German father who fraudulently obtained US citizenship (to avoid German taxes & military service) & a noncitizen mother. His citizenship was based on a technicality the #MAGA movement wants ended (for non-white people). He was no more American than Nicole Kidman (born in Hawaii).
I find adjudicating people's degree of American-ness pretty distasteful. Only one of my parents and one of my grandparents were born in the US. I'm still American. Trump is an abomination for many reasons. Where his parents were from or their citizenship status at different times is not one of them.
But it's not just his citizenship that's the problem. Because grandpa Drumpf died young, his German wife, who hated the US, raised her son not to appreciate the land that gave them refuge, but to see US citizens as marks. It's the combination that's so damning.
Ok, that's a reasonable narrative.