Congress can sue, or they can impeach. There is no debate on that. Can Pelosi sue, and can Schumer, or does it have to be Congress, as indicated by majority vote on a resolution?
IDK.
I think, in order to have standing in any court, you have to show specific, deliberate and unique harm. I think just asserting a lot of people are harmed doesn’t cut it. That would be a Class Action or maybe a RICO case. I don’t see where individuals, especially from an opposing political party, would have SCOTUS standing.
SCOTUS is limited to constitutional arguments, is that right? So, this would have to be a case brought over Separation of Powers or Enumerated Powers, again: IMO. Otherwise, it boils down to political differences and the SCOTUS doesn’t do politics, at least not publicly.
So, I think it has to be a Constitutional case brought to decide between Presidential and Congressional Powers. There must be a slew of decisions extant from the Lincoln Administration. Again, JIMO.