QUESTION: Art. 4., section 2 protects states from infringing on fundamental rights. It is my understanding that these are very narrow: right to travel, right to pursue common calling or vocation etc. My question is are the fundamental rights that are derived from substantive due process, like the right to marriage or right to privacy, protected as well by Art. 4.2?
ANSWER: Two response. First, I don't think the list of rights considered "fundamental" for purposes of Article IV, section 2 is all that narrow. It includes, for instance, the right to pursue a common calling, the right to own and dispose of property, the right of access to the courts, and a host of other things thought "important to the unity of the nation." Second, I would say probably, yes, to your second question, as that category is so much smaller. There are not that many rights that are so important -- "implicit in any scheme of ordered liberty" -- as to be "fundamental" as a matter of due process. Thus, it is likely true (though I'm not certain) that those rights that are fundamental under the Due Process Clause would also be considered a "privilege" or "immunity" for purposes of Article IV.