This is a simple cynical political ploy.
Grump knows he has no support anymore among anyone but the super rich and the ignorant poor, they are his only hope of retaining his presidency in 2020.
This tweet was a direct appeal to the white, bigoted ignorant people who think the only place for a black person is on the end of a chain or a rope, the only place for an Hispanic is in the bathroom with their arm round the U bend of a toilet and the only place for a middle easterner is in the cross hairs of their gun sight.
To these people none whites are not American, they are "other" and should aspire no further than the butlers pantry, to them Trumperdink is the second coming or Robert E Lee who will put the white people back where they belong and will as Mark 9:3 says make America "... shining, exceeding white as snow; so as no fuller on earth can white them."

And you know what? Thanks to America's unbelievably underfunded, dangerous and creationist ridden fundamentalist public school system, he might just be backing the right horse.