It only takes four votes to grant cert. In today’s American Tradition Partnership v. Bullock (Montana Citizens United Sequel), the Court denied cert and summarily dismissed the petition. Justice Breyer, joined by Ginsburg, Sotomayor, and Kagan issued this dissental (well really, they dissented from the grant–and reversal—of the petition, which is kinda  dissental):

 Were the matter up to me, I would vote to grant the petition for certiorari in order to reconsider Citizens United or, at least, its application in this case. But given the Court’s per curiam disposition, I do not see a significant possibility of reconsideration. Consequently, I vote in­ stead to deny the petition.

So the rule of four is trumped by five votes.

Anyway, it seems that Roberts, Scalia, Kennedy, Thomas, and Alito think that the dissenters doubts cannot be “serious.”

The question presented in this case is whether the holding of Citizens United applies to the Montana state law. There can be no serious doubt that it does. See U. S. Const., Art. VI, cl. 2. Montana’s arguments in support of the judgment below either were already rejected in Citizens United, or fail to meaningfully distinguish that case.

Update: A prof on the Con Law list serve writes:

It seems to me that the rarity of the 5-4 summary reversal on the merits in Bullock is largely a function of the odd choice that Justice Breyer made–to dissent from the grant of certiorari rather than to vote for plenary review… After all, if, as the tradition goes, four votes for plenary review will take precedence over five votes for a summary reversal, then that helps to explain both the dearth of 5-4 summary reversals (which can only happen when the dissenters opt for voting against granting as opposed to voting for plenary review) and the existence of a decent number of 6-3 results (which could conceivably happen any time there’s no fourth vote for plenary review).