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.

David Williamson owns shares of UnitedHealth. Follow David on Twitter: @MotleyDavid.

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