This is a great story for Federalism and the Constitution and also for demonstrating the limits of presidential power. This article discusses the county in Texas where only 12 people have signed up for Obamacare. In itself this is a fairly simple example but it does demonstrate a number of things.
It demonstrates the diversity of the USA, which is so crucial to federalism. It is so easy to forget that the USA is not really one country but a collection of at least 50. Think of the differences in accent, language and customs that exist across the UK and we are smaller than most US states! Therefore, this emphasises the importance of powers being retained to the states by the US Constitution.
It also shows the difficulty a President, and indeed federal government in the US, face. Just because they have passed a law, the size and nature of government in the USA means that the states will be required to initiate, run or enforce some of the laws that the national government pass. In this case Obamacare makes health insurance mandatory but the exchanges from which this can be purchased are operated by states. Therefore, while a state is unlikely to outright ignore the federal government, they may drag their feet or throw up roadblocks to the role they are expected to pay. In this instance, with only 12 people in this county signed up, realistically what can Obama do about it???! This is a great example of where the president can be weakened.