Since both Obamacare and most gun restrictions are unconstitutional I would say that the president has a duty to not enforcer those laws in any state Clearly, however the president cannot pick and choose which states will enforce a criminal statute and which states he will not.
If a president believes a federal law is in keeping with the powers granted to Congress, then his sole Constitutional duty is to ensure that the laws are faithfully executed. If he fails in that duty, as he has for instance on immigration laws, then that is an impeachable offense.
My arguments on this thread are addressed to the limited idea that Obama thinks he can grant a waiver of federal prosecution for criminal laws to one or more states, while continuing enforcement in all the other states.
Actually that would also be an impeachable offense. But the cowards in congress will never do that, so we have to try and survive until Ted Cruz is elected president.
I have to agree to the selective enforcement angle not going to pass muster. He could end not enforcing them in any state then to be even handed. There are many arcane and forgotten laws that go unenforced to.
The Latin American reaction will be interesting.