Obamacare should be thought of as a three-legged stool, but is one of those legs showing cracks?

While the Affordable Care Act is trying to accomplish a lot of initiatives, there are three, and really only three, aspects of the law that are irreplaceable. First, no discrimination by insurers for pre-existing conditions; second, the individual mandate to spread the increased risk from insurers to healthy customers; and third, exchanges to facilitate purchasing of insurance. Take one away, and the stool topples. Which is why some are reacting negatively to the news that Aetna (NYSE:AET) will withdraw from another state-based insurance exchange.

In this video, health-care analyst David Williamson discusses what these events mean for investors in Aetna, why it's withdrawing from five states, and what the implications mean for the future of Obamacare.