I’m reading David Potter’s Constantine the Emperor, partly just for my own edification but partly as “deep background” for the Trinity project I’m beginning to think about considering planning. The first third of the book is devoted to the state of the Roman Empire in the decades preceding Constantine’s rise to power (indeed, Constantine barely manages a handful of cameo appearances within the first 100 pages). One striking feature of Diocletian’s reign is the use of power-sharing as a way of managing the sprawling Empire. Eventually Diocletian had a co-emperor to whom he was formally equal (both being titled Augustus), then two sub-emperors who also shared power (termed Caesars). Diocletian still maintained a certain primacy over his fellow Augustus, but he was at great pains ideologically to assert that power was not divided, but shared among the four.
In “Monotheism as a Political Problem,” Erik Peterson famously declares that the Trinity renders political theology impossible because the inscrutable mystery of divine triunity has no possible earthly analogue. I have a healthy dose of Barth in my theological background, so I see where this is coming from, but I think it’s basically wrong. There are plenty of political analogies for a power that is shared among several persons while deriving from one of them and remaining undivided. We can see something like this in the rise of a powerful vice-president in recent American politics — a VP can often function as an effective co-president (or supra-president, in the case of Dick Cheney). Other figures might gain similar stature, as Rahm Emanuel and Timothy Geithner arguably did in the early years of the Obama administration. The legitimacy of the administration derives ultimately from the elected president, but someone with the implicit trust of the president shares in and extends the president’s authority rather than competing with it. (Or at least that’s how they present things for public consumption.)
The Fathers at Nicea would have had personal experience of such a regime. I don’t want to be reductive about this, but I also don’t want to claim that questions about the divine governance of the world — particularly questions that are being adjudicated in a politically-charged environment, at the Emperor’s behest — exist in splendid isolation from questions about human governance. (Once developed, of course, theological doctrines maintain a certain autonomy and can have unanticipated effects, as in all the liberation and other politically radical theologies that have drawn on the Trinity as a rebuke to worldly powers.)