On the one hand, Rome lasted a few hundred years after the end of the Republic. On the other hand, events move more quickly and processes play out much faster these days. The Soviet Union lasted a mere 70 years, for instance.
One thing I think we can be sure of is more state/emperor worship and proliferation of worthless liberties and distractions as substantive liberties are more & more curtailed. Bread (Obamacare) and Circuses (gay "marriage" & suchlike) will supplant liberties such as freedom of religion & expression and the whole panoply of natural and civil rights that are a threat to gov't power.
Our 21st century equivalent of 4th century German barbarians crossing the border in search of the wealth and opportunity of their more prosperous neighbor are the illegals pouring over our border. Individually, no more malignant than any group. Collectively, a huge threat to our culture, economy, and limited gov't.
Sadly, our rulers really do not like us. BHO is not the only one and the Democrat party is joined by many in the Republican party who would replace us with a more biddable & dependent population.
Electing a McCain or Romney or Rubio will not arrest these developments. Politics won't save us, as policritters do as they will, COTUS be damned. Only a new Great Awakening or moral renaissance as occurred in Georgian England will do the trick, as the fault lies with us, in that we have become accustomed to dependency and license. Our founding fathers understood the limitations of self-gov't and a population of teat-sucking libertines glued to the couch are not up to the task.