Obamacare explained: why healthcare reforms could determine future of US politics That is why the case is also being seen as a much broader referendum on the future size and direction of American government and will be a recurring theme in this autumn's general election. That's politics, not law. How is any of this illegal? The main legal challenge is that the ACA mandates everyone, by law, to buy health insurance - "the mandate" for short. Opponents say that this violates the US Constitution. If you can force someone to buy healthcare, the argument goes, why not broccoli to make kids healthier, or American cars to improve the economy? To which supporters reply that logic is specious: under the so-called "commerce clause" the US government has the right to regulate commerce nationally. The "broccoli argument" is moot because healthcare is not a choice, everyone needs it as a condition of being human, of living and dying. They add that if there is to be a challenge it should be through the ballot box - ie by defeating Mr Obama in November, since Republicans have pledged to repeal the law - not in an unelected court. Any other challenges? The law also requires all states to expand the safety net for the poorest Americans - Medicaid - for everyone with incomes at or below 133 per cent of poverty level. Several US States say this infringes "states' rights" to sovereignty on this issue. What might the court decide? It could uphold the ACA, it could strike the law down, or the justices could do something in between, like upholding the law but declaring the "mandate" part unconstitutional. Whether the ACA can function without the "mandate" is the subject of a separate argument. A final option would be to kick the whole thing into touch before the election - "the punt," in US legal parlance. This ruling would find it is illegal under US law to review a tax before it comes into force (The Anti-Injunction Act), but would depend on a separate argument over whether the ACA, which comes into force in 2014, is indeed a tax. What's the likely outcome? Dangerous making predictions, but the consensus is that the Supreme Court will probably uphold the law. The nine-member bench is split 50:50 between liberals and conservatives, but in the past healthcare is not an issue, like abortion, that has fallen along strict ideological lines. Legal pundits also predict the Supreme Court, as the unelected portion of the US legislature, will be wary of being seen to meddle in the democratic process by striking the law down before the election.