I've been working much of late on Southern constitutional ideas at the time of secession -- what particularly interests me are how much constitutional ideas were raised in debates about what the South should do next. Of course slavery -- and the centrality of slavery to southern culture and economy -- were at the absolute center of the debates. But what interests me are the ways that Southerners turned to constitutional arguments to support their case for disunion (as in the North had repeatedly violated the proslavery constitution and that justified secession) and how they argued in constitutional terms (the constitution both permitted them to secede and also that they were reacting in the same way as the American revolutionaries who had a right to determine their own government). As for many conservatives, constitutional arguments framed Southerners' world -- this makes a lot of sense because constitutions typically limit the actions of radicals (they constrain action against slavery or property, for instance).
But what interests me right now is how infrequently historians talk about the constitutional dimension of secession. This may be because historians typically focus on core causes, such as fear of economic losses and of social upheaval, rather than the format in which those core causes are expressed. For many historians, constitutional arguments are the language rather than substance. While I certainly understand -- as did pre-Civil War Southerners -- that constitutional arguments by themselves had little independent interpretive bite, ignoring constitutional arguments is unfortunate for a couple of reasons. First, the constitutional arguments help us understand how they were framing the issues. They contributed to a clarity of thought to for the Southerners, such as how they understood the particular concerns about Northern threats to slavery. Second, the constitutional arguments -- particularly when recognized by the Supreme Court -- provided support for the Southern attitudes. That is, they legitimized, much as we think Brown legitimized the Civil Rights movement a hundred years later, Southern politics. This is worthy of a lot more exploration sometime soon -- especially given how much Southerners spoke about the Supreme Court during the secession winter. Third, and perhaps least important, I think that the constitutional arguments provided some shape to the Southern complaints -- that is, they may have provided some frame for thinking about what Southern states' options were -- such as what states needed to show in order to justify secession.
I want right now to add one other hypothesis to those above for why historians don't talk more about constitutionalism -- perhaps another reason we overlook constitutionalism is because historians have paid attention to the documents most easily available. Those are not ones that typically focus on constitutionalism. This has changed somewhat recently -- William Freehling and Craig Simpson's volumes on Georgia's secession debates in late 1860 and the Virginia legislative debate in the spring of 1861 both have substantial discussion of constitutionalism; and Jon Wakelyn's Southern Pamphlets on Secession. But for the several generations before the leading documentary collection on secession was the 1931 volume by legendary Michigan historian Dwight Lowell Dumond, Southern Editorials on Secession. I've been reading those closely of late and am increasingly interested in Dumond he selected editorials that fit with his interests in discussion of politics around secession. I completely understand his point -- when I edit a collection of literary addresses at southern schools before the Civil War I'll probably tilt the collection towards those that deal with legal thought and jurisprudence. However, I think subsequent historians using Dumond's collection may not have realized that there were other themes, like ideas about how the North was violating the Constitution (in the mind of Southerners) and how those violations framed the response. For those ideas were not represented in that volume -- or at least not much represented. Here's a link to several of the editorials in Dumond's volume that do talk about constitutionalism.
There may be another reason why historians don't focus on constitutionalism -- because paying attention to the ideas of constitutionalism may smack of nullification and interposition. That is, if we take seriously the arguments of the South in the years leading into Civil War, so may think that we legitimize the arguments heard frequently in the 1950s and 1960s in response to the Civil Rights movement. I don't suppose anyone thinks historians these days are legitimizing those arguments, but I wonder if that's one of the reasons why we have not focused on the centrality of those arguments leading into Civil War -- or, relatedly, by focusing on constitutional arguments that may look like we are relocating the core cause of Civil War from slavery to states rights. Of course, the right of the states that was being protected was the right of slavery and of the states' slaveowners. But I think this may explain some of how the historiography of secession has been bent by the ideas and work-product of historians.
The image is of the south gate of the old state capitol in Milledgeville, Georgia, from the Library of Congress' historic building survey.