Just giving some thought to this case, it's actually stunning how frivolous it is. This is a challenge to a law passed by Congress pursuant to express authority in the Constitution (15th Amendment). There is no basis for challenging it except on the barest of due process grounds: that it has no rational basis, i.e., there is no rational connection between the law and enforcing the right of US citizens to vote without racial discrimination. I honestly don't know if this fundamental due process argument has ever won in any context. Most judges dismiss the argument out of hand (or ignore it entirely).
Mind you, the law being accused of having no rational basis passed in 2006 by a vote of 390-33 in the House and 98–0 in the Senate with Republicans in control of both houses and was signed by George W. Bush. The argument is that all of these people acted irrationally in passing it to enforce people's right to vote without racial discrimination. And the SCOTUS is seriously considering crediting that argument. These are extreme times, with extremists in positions of power threatening to do serious damage. I can't even really convey in words the level of frivolity of the argument being made.
Unfortunately, the current SCOTUS has already severely undermined the 15th Amendment by interpreting it as narrowly as possible. Absurdly so, in fact, holding that it is constrained by the 10th Amendment, which of course is ridiculous since the 15th was passed later in time. The Roberts Court effectively read federalism into the Amendment where it doesn't exist. This court is really disgusting and incorrigible.
By the way, I know a lot of liberals thought John Roberts was a cute and cuddly centrist during his confirmation process, but he's actually a vile racist, probably the vilest on the court. He wrote anti-integration memorandum when he was part of the Reagan Administration.