Here is a comparison between the history of Rome and that the US. After a point it wanders in to some goofy future history, still worth a read. In one the footnotes there is examination about how the Romans liked things legal and constitutionally even when slipping into empire.
The major accomplishment of Augustus was to organize the Roman government in such a way as to make monarchy palatable to such diehard republicans as the Romans. He couldn't just declare himself king. That would be political suicide. Imagine the outcry -- even among capital-R Republicans -- if George W. Bush held a coronation with a crown and purple robe in the Lincoln Memorial.