Obama is the Caesar, cabinet secretaries are analogous to Roman governors, and the Roman dux to our czar.The dux, though, isn't necessarily loyal to the Frankish king, if this year's story arc in Vikings continues. Rollo has the local authorities crossbow his temporarily not nomadic subjects, but there's likely to be more side-shifting as the season progresses.
The part of this that is missing (and I'm not expert enough to add it) is that under the Franks, a dux was named as the local (and loyal) representative of the Frankish king to rule over captive peoples who were still tribal, but while no longer nomadic didn’t really have a fixed geographic region either (for example Chrodobert was dux of the Alemans in the 7th century).
SUMMIT CAUSEN, SUMMIT DUX.
An oldie from Voluntary Xchange suggesting that special advisors to the president get a title other than "tsar."