A few weeks ago SCOTUS heard arguments in King v. Burwell, the latest Obamacare case. SCOTUSblog describes the argument in Plain English. Cristian Farias in Slate emphasises the most interesting point, Sotomayor May Have Saved Obamacare
Apparently the federal government can't write laws that coerce the states. Bond v. United States came to the court twice, Kennedy writing one opinion, Roberts another. Sotomayor points out, “We said [in Bond] that it is a primary statutory command that we read a statute in a way where we don’t impinge on the basic federal-state relationship.” She pointed out that offering the states a choice, either setup your own exchanges and get subsidies or use the federal one and don't which results in a death spiral of the whole system isn't really a viable choice and is therefore coercion. Kennedy asked questions following up on this and Roberts remained silent. We'll probably hear something about this line of reasoning in either the opinion or a dissent.