The latest turmoil in health insurance marketplaces created by the Affordable Care Act has emboldened both conservatives who want to shrink the federal role and liberals who want to expand it. UnitedHealth Group announced last week that it may pull out of the marketplaces in 2017 after losing money this year. This followed the collapse of 12 of the 23 nonprofit insurance cooperatives created with federal loans under the health law. In addition, insurance markets in many states are unstable. Premiums are volatile and insurers say their new customers have been sicker than expected.