Substantive antitrust law has dramatically shrunk. The shrinkage, which began in the 1970s with the transition from the Warren Court to the Burger and then Rehnquist Courts, has accelerated in the last decade. Much of the shrinkage has to do with the expansion of the rule of reason and its displacement of per se rules. The Supreme Court has gone so far as to state that it “presumptively” applies the rule of reason while per se illegality is limited to a “narrow category of activity.”
It is axiomatic that the rule of reason has an inverse effect on the breadth of Section 1 of the Sherman Act (Section 1). Rule of reason cases are far more difficult to win than are per se cases and are thus much less frequently even initiated. Instances of actual antitrust liability are significantly reduced even among cases that are litigated. Thus, the broader the rule of reason, the more limited is the reach of Section 1. The result is fewer wins for private plaintiffs, who often cannot prove the market effect required by the rule of reason. In addition, the Supreme Court’s Twombly and Iqbal decisions have wrought more exacting pleading requirements to state a viable Sherman Act claim.