View: No, UnitedHealth doesn't spell the end of Obamacare

None of this is to say that there aren't improvements the government could make to help insurers navigate the exchanges. Congress anticipated that, in the early years, insurers would struggle to anticipate their medical costs, and that as a result they would set premiums too low and thus lose money — exactly the problem that UnitedHealth is now reporting. That's why the law established a series of buffers against losses, which Congress could extend or expand.

The government could also require that most people buy coverage only during the regular open-enrollment period. UnitedHealth said those who get insurance outside of that period tend to use more services, increasing its costs.

Finally, the government can and should do much more to encourage the young and healthy to get insurance. It's not as if they don't need it — accidents and illness don't discriminate on the basis of age. More young and healthy customers would make the risk pool more attractive to insurers.

The exchanges face some real challenges. UnitedHealth's announcement doesn't make failure any more likely. It just reinforces something that should already have been obvious: Obamacare still needs some work.

—Editors: Christopher Flavelle, Michael Newman.