The U.S. Justice Department’s victory on Thursday in its lawsuit against the credit card company might give merchants more leverage in their effort to cut the costs, which are largely hidden from consumers, and is the latest in a series of blows to the New York-based firm after partnerships with Costco Wholesale Corp. and JetBlue Airways Corp. ended. American Express failed to show that its so-called non-discrimination provisions, imposed on merchants who agree to accept its card, don’t harm competition, U.S. District Judge Nicholas Garaufis in Brooklyn said in his ruling.