As health insurers head for the exits, Americans who have been whipsawed by ObamaCare may get whacked again this fall: First, they were thrown off private plans that were declared illegal, then they were forced into the ObamaCare exchanges, and now they could face the prospect of being shut out of coverage through their exchanges entirely for 2017. In Arizona’s Pinal County, for example, no insurers are offering coverage through the exchange. While decisions won’t be final until next month, people in other counties could face a similar fate.Elsewhere, millions of Americans will have a “choice” of just one carrier,...