I wouldn't have known it was a Nazi symbol myself. I can't recall ever nothing that specific symbol in WW2 stuff and I like to think I'm pretty well read.
Also, if true, it seems like he's known what the tattoo was for at least a decade
https://gamefaqs.gamespot.com/a/forum/c/c770e093.jpg
Trump is pursuing a chaotic far-right overthrow of existing US government norms and checks and balances, trying to destroy our way of life.