“Why will Grayson have standing? Can he show damages?”
A California or NY judge will give him all the standing he wants.
They might want to, but after all the "no-standing" rulings from higher courts when Barry Sotero was challenged, they would be demonstrating contempt for the previous rulings and duplicity. Unless they can show that Grayson is or could potentially suffer damages personally, I think it is a no-go.
If Trump is so concerned he might be able to show personal damages as a rival candidate. I think that he could be a plaintiff and bring suit, but at great political risk, so he will probably just keep making snarky innuendo.