UnitedHealth Group signage is displayed on a monitor on the floor of the New York Stock Exchange.Shares of major health-care companies fell as much as 5% on Wednesday as investors feared pressure from lawmakers and patients could force changes to their business models.The declining stocks include UnitedHealth Group, Cigna and CVS Health, which operate three of the nation's largest private health insurers and drug supply chain middlemen called pharmacy benefit managers, or PBMs. They also own pharmacy busine ...