He's dog-whistling about Black people and minorities in general, obviously he's not gonna say or call out such races and ethnicities because that's just bad PR and while he may be stupid, he's not that stupid to say it like that and let alone the people behind Trump would advise him not to go all out like that.
So instead, he's whistling, and his supporters know exactly who he's talking about or who comes to mind from reading this quote

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Some of y'all dudes on here who are on this “American over everything” are gonna learn the hard way that all that shouting and boasting about being American while draping yourself in the American flag, acting all superduper patriotic, doesn't hold the same weight when you're Black.
White people can go around comfortably shouting and boasting, but Black people don't have that same luxury.
As the saying goes “if they could, they would”. That's the only thing preventing them from acting out on these fantasies, but if they were able to manipulate the Constitution, etc, without pushback, legalities, etc, they would.