Tuesday’s announcement by the Minnetonka, Minn.-based UnitedHealth Group that it will withdraw from most of Affordable Care Act (ACA) health insurance exchanges it operates in is perhaps the single biggest jolt yet to the government program. As the company pleaded inability to continue in those state health insurance marketplaces because of losses, the focus has shifted to whether other insurers would follow that path, and the need for the industry to find new marketing and risk-pooling strategies. UnitedHealth’s insurance arm, UnitedHealthcare, is staring at losses of more than $1.1 billion in the state health insurance marketplaces between 2015 and 2016, according to its chief operating officer and chief financial officer Daniel J. Schumacher.…