You could add whatever case you see as most harmful or representative when it comes to legalizing having to show a voter ID at polls, given that this disproportionately hurts black and other minority voters.

SCOTUS has upheld voter ID laws on a state-by-state basis when they've come before it. But, as a nonlawyer, I don't know if one set the precedent or is more important than another.

Alabama has added to the problems by closing dozens of DMVs (where you get your photo IDs), many in majority-black districts while denying that it had anything to do with race and saying it's reopened some ... one day per month. Here's what the ACLU said about the initial closures:

https://www.aclu.org/news/voting-rights/alabamas-dmv-shutdown-has-everything-do-race