Had the continental congress elected a king the title is not unlikely to have been changed to emperor, once the nation grew westwards.
This is how the flags of such an empire could have looked like.
America is a lot like the Romans as it is. I could see it degrading into something kind of like a mix between the Roman and British Empire.
the people's republic of california
I know, it's hard to believe that we actually have elections and the president must still abide by congressional legislation.
Full credit to you
the tyranny of king Washington!