After 450 AD the Goths and the Huns had an electoral lock on the Western Roman Empire too

Ross Douthat points out in the NYT the that the key to Democrat electoral success is social and economic decline.  The more families dissolve, the more isolated minorities become, the more people become dependent on the dole, the more the Dems win.  And IMHO, the more the Dems win, the more families dissolve, the more isolated minorities become and the more people who join the dole.  I wouldn't quite call it a virtuous cycle - but it's certainly become a successful one.

Forward!