He feels wronged, so he's doing what he can to hurt others as revenge.

This will affect the ENTIRE Nation one way or another. It really feels like a damn YA Post-Apocalyptic novel... We're on Chapter 2 and just figuring out who the main characters are. Hint: The Heros are a Doctor and the staff at his Hospital and probably his 16 yo daughter (you know, YA novel)... the villains are of course, the President and his team. Somebody is probably already writing this drek as we speak... wait, that was me... Sorry.

But really, to return to the premise. Why does Donald Trump want to kill as many Americans as possible? Especially the elderly? What could he possibly have to gain?

the performance of the stock market, and he's stupid enough to think that if everybody just goes back to work the economy will magically recover. He doesn't listen to, or care about, the opinions of the experts who tell him that this will cause many more people to get sick and possibly die. He probably doesn't believe them, because if he did he would realize that older people are a large part of his base. Why would he want to kill them off? He doesn't; he just doesn't believe the scientists because he wants the market to recover.

He's just too stupid to understand how poorly he is at responding to this catastrophe. He surrounds himself with sycophants and yesmen... but still, we're talking MILLIONS of American lives at stake here. The sycophants and yesmen have families too. People have to have told him repeatedly that this is all DEADLY serious. He is truly delusional i guess.

... times

Brad Parscale. Stephen Miller. Probably a bunch more in the shadows. Trump is the head salesman, the rest feed him the product. Trump kissed off the old folks from the beginning by dissing Bush and McCain. Bannon convinced Trump to go after the younger guys. So, I certainly don’t think Trump cares a shit if the elderly die. He lost them as voters.

His religious influencers are working overtime now to keep that block intact.

he has nothing between those ears but a massive ego. All his decisions are based on 'self'. I would feel sorry for any other human with such massive insecurity issues, but he passed the point of pity a long time ago. Now he needs to be contained, and quarantined. The GOP produced him, but that doesn't make him less deadly.