This 5-3 ruling comes as part of a string of decisions by the conservatives on the court blocking lower court rulings that would have made it easier to vote during the coronavirus pandemic. But hidden within the main concurrence written by Justice Brett Kavanaugh are two threats much greater than overturning six extra days for ballots to arrive by mail: He explicitly endorsed legal theories that could help President Donald Trump stop the counting of mailed ballots after Election Day or, worse, override results with the help of Republican state legislatures.
This should have all been thought through and worked out at each state. Mail in dates set beforehand. This is very "after the fact".