"The Times, Places and Manner of holding Elections for Senators and Representatives, shall be prescribed in each State by the Legislature thereof; but the Congress may at any time by Law make or alter such Regulations, except as to the Places of chusing Senators."
Then they need to challenge it at the time they are changed, and not after the election regulated by those laws have already happened. You could still challenge them now, but it would flagrant assault on democratic principles to use this as an excuse to not count votes cast according to these rules.
There have been plenty of much more questionable elections in the past. 2000 is a big one. In 2004 there were a lot of hints that Diebold voting machines favoured Republican candidates. Still, those elections stood, because the votes had already been cast. If rules are unfair, change them, but don't demand the election gets blindly thrown your way for no good reason.
> It’s a violation of the constitution for an individual state to change voting laws like that
I mean, while we're making stuff up, lets say it's a violation of the constitution to allow for a Democratic government. Article IV, Section 4 requires Republican party rule. /s
Which federal law do you think they violated?