Actually, at least in terms of the law, SCOTUS has done no such thing. It says repeatedly that its refusal to grant cert has nothing to do with the merits of a case.
In this case, SCOTUS, in Bush v. Gore, laid down the law, and a lower federal court is perfectly capable of enforcing it. Let us see what happens to the absentee voters' suit in federal district court in Trenton.
My guess is that the lower court will determine that sufficient harm was not demonstrated. They got the signal from above not to further mess with this case.