Yes, and both came from within the established regime. One political, one military. In neither case, was it necessary for the citizens to revolt to oust the dictator.
With the threat Obama's become to his party, I can see the possibility of a cabal forming within the Democrat establishment to destroy him politically, in a bid keep him from doing further damage to the rest of their party. That could (but probably wouldn't) include impeachment.
The scenario of him being ousted by the military is, in my opinion, less likely, but still possible. It all depends upon how far he over-reaches in his quest for complete power in the next three years. If he tries to invoke martial law for any reason, that would be the likeliest trigger.
-——the military-——
I wonder if there is “the military”
After 5 years is our officer corps a homogeneous entity?