QUESTION: I was just wondering if you could clarify for me the difference between  national citizenship and state citizenship as applied to the privileges and  immunities clause. I am confused on the distinction because both the Privileges and Immunities Clause of Art, IV, Sec 2. and the Privileges or Immunities Clause of the 14th Amendment discuss this idea of  "fundamental rights," or what is vital to the nation as a whole, so I am  wondering what the distinction is. 
 ANSWER: Actually, the Privileges or Immunities Clause of the 14th Amendment  does not protect such "fundamental"  rights--rights that bear on the vitality of the nation as a whole. The fact that states (and not the federal government), prior to the Civil War, were primarily responsible for protecting such "fundamental" rights was a critical part of the reasoning in Slaughter-House, as the  majority believed it unthinkable that the new amendment would afford such protection. But these rights are not protected by the Privileges or Immunities Clause of the 14th Amendment. Indeed, that they are not so protected was the critical point of the Slaughter-House decision.
 QUESTION: If something is vital to the nation as a whole (like not discriminating  against out-of-state residents for job qualifications), then how is that  something dealing with state versus national citizenship since it applies to the  "nation" and not just the state? 
 ANSWER: I may not fully understand this question. If the right at issue "bears on the vitality  of the nation" as a Union (whatever exactly that means, it is a "privilege" or  "immunity" within the meaning of Article IV, section 2. But this does not mean  it is covered by the Privileges or Immunities Clause of the 14th Amendment.
 QUESTION: Also, it seems to be that the law overruled in Saenz v. Roe dealing with  residency requirements seems to be more applicable to rights under state  citizenship, since the individuals discriminated against were already state  residents, whereas in the P and I cases we read under Art. IV, sec 2, we were  dealing with individuals who were out of state being discriminated against.  
 ANSWER: Saenz did concern a "right," in the first instance, created by state positive law --  namely, the right to TANF payments. But the right actually vindicated by the  Supreme Court's decision in Saenz was the right to interstate travel--or, more specifically, the component of  that right that encompasses the right to interstate migration. This right is  a right incident to national citizenship, not state citizenship. So the holding  of Saenz is that a state cannot discriminate in the allocation or protection of  state legal entitledments (whether we call them "rights" or something else) in a way that interferes with this national right of interstate  migration.Thus, any discrimination among citizens based on the duration of a citizen's residency will be subjected to something akin to strict scrutiny.