I can't say why the president tweeted this. He might be trying to entice the far left to attack this golf course so he can scare the rich pricks there into donating money. I have no idea, I need to let a day or two go by so more information can fall out of the news cycle
Pure speculation:
I don't think Donald Trump has secret meetings with white nationalists to actively plot genocides or whatever. I am not sure I can say the same about parts of his administration.
But I think he's aware those people exist and they support him. Not just them, but:
antivaxxers
flat earthers
evangelicals
bad cops
jim crow southerners
Honey Boo Boo fans
Info Wars types
kkk
...so forth and so on. This is just incontrovertible truth. They certainly aren't voting for Joe Biden or independents. I do believe Trump is a narcissist and therefore doesn't have values with enough depth to give a fuck about what those types represent. To him, all that matters is that they're a demographic in his base -- a block of voters and viewers that directly effect his ability to keep building his brand: himself. I don't think he sees any consequence as too small in achieving this. So while he may not actively want what they want, he doesn't give a shit if they get it and probably sees himself as making 'great deals' with them via policy in exchange for continued support. He's doing something to keep his voters happy and it isn't economic prosperity and opportunity for the working class. Anybody can see that overclocking the economy with deregulation is not the same thing as fixing structural problems that will have lasting effects.
The recession is going to hurt bad. The worst part is, it's the typical, life-of-quiet-desperation voter who isn't an overtly bad person that's going to get fucked over the worst. I think they know deep inside the absolute best outcome of his presidency is a pyrrhic victory in the culture war. Trump isn't going to make America great again and they know it, but he might help the left go down with the ship. In the end, they'll still live in the mess he's helping create in exchange for saying...they voted for him. And maybe the GDP did better. "Great deal", indeed.