Obama "chose" not to enforce federal law and the state took it upon themselves to reach into jurisdiction that does not belong to them. You may disagree w/Obama's decision not to enforce the federal law, but you can't disagree over the state's overreach here. Yes, the states are undoubtedly trying to frustrate federal immigration laws in the case (as some states disagree w/the new admin's stance), and they are well within their right not to follow the feds on this. Your federal background check analogy is bunk because not forwarding a federal background check to the feds constitutes a violation of the constitutional right of citizens to bear arms, as the background check is a necessary step into getting one. Not doing so would be the state infringing on a citizen's rights. Same reason voter ID laws keep getting shut down. You don't like it, change it. You could make a case for instance, that by not enforcing immigration it somehow hurts corporations' earnings and that corporations being people too (read citizens united) the states are infringing on their 14 amendment.
I don't understand how you can argue so unequivocally. it makes your whole argument political. you should state per some sup ct decisions its you opinion Arizona was reaching into jurisdiction that does not belong to them. However, its not so clear to me Arizona is excluded from keeping illegal citizens out of its state when the FED govt was acting arguably unlawfully under Obama. Its not clear to anyone that many of things Obama did with respect to immigration were constitutional. its also not clear that states are allowed to set up sanctuary cities and impede or not cooperate with the federal govt in the area of immigration. This whole area is ripe for litigation and we will have at least 1 new supreme ct member.
His entire argument is absurd. Clever, but absurd. The preemption doctrine does not come into play unless a state is pursuing a policy that conflicts with a legitimate federal responsibility. Arresting illegal immigrants who are in violation of federal law does not create a preemption problem any more than arresting a bank robber does, since bank robbery is a federal crime. Sanctuary cities are violating numerous federal laws, eg by aiding and abetting immigration violations, social security fraud, identify theft, etc. This is not a situation like the pot laws where some states are just not enforcing federal law. These sanctuary cities are actively impeding the work of ICE by ignoring federal detainers and failing to report illegals.
If cities are actively impeding a federal investigation, then they are guilty of aiding and abetting. But the failure to enforce a law isn't aiding and abetting.