I have been reading a lot on Augustine and politics/law/society lately, hoping to write a piece on the topic. But with a baby, classes starting soon, and too many other projects currently in the works, I don't know whether this paper will actually see the light of day. In any case, I thought I'd jot down a few of my thoughts from the bit of research that I have done- just a few musings about Augustine and the political rather than some grand idea. Only 3 theses worth expanding upon are coming to mind at the moment, so that's all you get. Maybe I'll add more in the comment section as they come to me:
1. Augustine and various Augustinianisms are each in their own right positively mammoth traditions to consider. A blessing (and curse) of being such an ur-figure like Augustine (or Plato, Aristotle, Hegel, etc.) is the possibility for so many permutations in readings and appropriations of an original system of insight. Just consider what large swaths of ground a label like "political Augustinianism" covers... from Orosius to Otto of Freising, Giles of Rome to Luther, to Reinhold Niebuhr and John Milbank. I think that critics of Augustine and his heirs should certainly address areas of inconsistency and disagreement, but there should also be a recognition that fruitful intellectual development results from the very different strands of interpretation that inevitably arise. At a certain point every thinker must abandon their traditio to posterity and providence, wherever that might lead. So, while I find it important to remain a student of Augustine and his own contributions, I think it is also legitimate to recognize one's commitment to a particular Augustinianism (or Marxism, or Platonism) without feeling a necessity to walk lockstep with its namesake.
2. Folks should stop talking about the "Constantinian" Church. Much as I love the Anabaptist bloggers out there, the term has become horribly over-used and applied to any situation where someone might deem church and state too intimate bedfellows. Scholars will employ the term loosely as well- I've even run across it in John Rawls. The problem isn't that there was no Constantinian legacy to deal with as a matter of political theology, but that such a blanket identification... usually meant to cover the entire period from the fourth century to the rise of the modern nation-state... is simply nonsense, a vacuous claim and a misleading characterization of the Church's history. Even between Constantine's reign and Augustine's episcopacy, there were significant changes in imperial policy and relations between Church and empire. Augustine himself deals with a Theodosian enthusiasm and its aftermath when Rome is invaded by the Visigoths- Ambrose before him deals with the Catholic zeal of Maximus, who executes a heterodox clergymen against the wishes of orthodox bishops quite in agreement with him on the charges. In neither case is the Church in collusion with Empire, Constantinian or otherwise. Constantinianism should be recognized as a watershed moment in the history of the Church, but only with a recognition of the significant vacillation in ecclesial and civil policy ever since; Constantinianism as a myth (as in the Donation of Constantine) should also be recognized as a necessary consideration for assessing the medieval period, but only with a recognition of its status as political myth and textual forgery.
3. R.A. Markus is misunderstood. The thesis of his classic study Saeculum, that Augustine introduces to the Christian theopolitical imagination a conception of "the secular", does not seem to me to argue for a bifurcation along the lines of a secular and sacred civitas. Those of the trendy "post-secular" persuasion will latch on to Augustine's famous statement from de civ 19 that "there is no republic" and interpret a theopolitical agenda that seeks to disarm any civil authority whatsoever as illegitimate insofar as it falls short of the Church's ability to foster true sociality through neighborly love. Markus' point about Augustine is not nearly so ambitious as to oppose any secular realm to a sacred ecclesial one (on the other hand, those who criticize him tend to err in overly sacralizing the ecclesial and picking a fight where there shouldn't be one). The idea of a secular age in Markus is that from Jesus' first coming to His second, the world exists in a time where no unambiguous claims to divine providence can be made... the secular is opposed to heilgeschichte, the conception of "sacred history" that is legitimate in the canonical historiography of the Scriptures but not as applied to any regime in our own day. The "secular" so understood is certainly reinterpreted to other ends in Augustine's heirs (see my thesis 1), but Markus' reading of the secular does not need to imply either ecclesial complacency before civil authority or an unholy alliance between the two "cities" for political ends.