Lyle links to the order. I had thought this case had a pretty good chance of being granted, as it raised some very interesting issues about modification of long standing consent decrees in the context of a meaty political dispute.
The effect of the cert. denial is to keep the consent decree barring the RNC from engaging in certain “ballot security” measures in place. The ruling prevents the RNC from engaging in certain activities, such as organizing poll challengers, etc. But the ruling only applies to the RNC, and does not stop state parties (such as the Ohio Republican Party) or non-party groups on the Republican side of things (such as True the Vote) from engaging in the same activities. So keeping the ruling in effect likely will not have large consequences in the voting wars.