The notion that federal government officials are necessarily opposed to efforts by states and local communities to nullify federal law is provably wrong. In fact, there is one area of national policy where the fedgov actively encourages nullification.
We are talking "sanctuary states" and "sanctuary cities" here. Over one half of US states either provide "sanctuary" to illegals outright or contain cities and counties that do: You can see a map by following this link.
Federal law prohibits entry into the US without a proper passport and visa or other entry permit. Since the fedgov actively encourages local violation of its immigration laws, how can it argue that other areas of the law are "off limits" to nullification?
What's good for the federal goose is also good for the local gander. This brings into play what is known in equity (a legally recognized doctrine based on moral concepts of fairness rather than positively enacted and case-specific law) as the "doctrine of unclean hands". After consciously and deliberately allowing this practice to continue for this long, the fedgov cannot now be heard to complain when state and local governments take it up on the offer and use the principle of Nullification to resist the enforcement of other federal laws. In essence, it has "waived" its argument. It is "estopped" from making its claim in any court of law.
There is no federal law that actually authorizes local communities to establish sanctuary to illegals. That means sanctuary communities are illegal. The federal government's open acquiescence to this blatant violation of its own laws in the area of immigration - and therefore of national security - therefore prevents it from opposing such efforts in other areas - like health care.
It would probably be helpful for those state attorney generals that are currently embroiled in legal battles with the federal government over their efforts to nullify Obama(Don't)Care, for example, to use this argument to their advantage. It will be very interesting to watch federal courts scrambling to craft a line of legal reasoning that would support the federal government's not only illegal but contradictory practice.