Gallup does a great service in tracking the decline in the uninsured rate state-by-state since ACA implementation. But they draw a misleading conclusion from their latest data set:
Collectively, the uninsured rate in states that have chosen to expand Medicaid and set up their own state exchanges or partnerships in the health insurance marketplace declined significantly more last year than the rate in states that did not take these steps. The uninsured rate declined 4.8 points in the 21 states that implemented both of these measures, compared with a 2.7-point drop across the 29 states that have implemented only one or neither of these actions.
In fact, the superior overall performance of these states in reducing un-insurance is due entirely to the Medicaid expansion. Collectively, their exchanges did not perform particularly well with regard to enrolling subsidy-eligible residents in private health plans.