The court’s ruling spelled major trouble for Visa and MasterCard. Under U.S. law, a competitor that has been damaged by the anticompetitive practices of dominant firms can recover triple the damages that actually occurred. Rivals Discover and American Express filed suits against Visa and MasterCard. In 2008, American Express reached an agreement with MasterCard for a settlement of $1.8 billion. That followed a 2007 settlement with Visa for $2.1 billion. Together, the two agreements represente...