Partisanship isn't really
that bad considering parliamentary governments get away with ignoring the other side all the time.
The only thing to worry about is if the GOP is dumb enough to be permanently marginalized. If the Republican dominance between the American Civil War and the Great Depression is anything to go by, it'll just mean the Democratic party will become
hilariously corrupt. More so as business interests migrate to where the power is.
Pure partisanship is nasty, but our system of government basically necessitates it. Until we move to a system where a spectrum of positions can get representation, you pretty much have to choose the side you think is closest to your own ideals and go for it, or throw your hands up in disgust.
The First Past the Post system precludes this from happening. Even in parliamentary government that use it, such as the UK or Canada, only have two really viable parties.
Really, even in proportional representation where third parties have much more influence, there are usually two dominant blocs. More voting power > ideological freedom of its members, usually.
Also proportional representation's benefit of stronger third parties is also its weakness. The splitting of "extreme" elements removes any moderating force. This isn't necessarily a bad thing, but a separate Religious Right party would gain a few more crazy points and would
still be courted for their valuable votes.