It's interesting to note that George Washington always publically stated that the two party system would end up tearing our union apart, (although he may have inadvertently had a hand in creating it.)
I think they act in tandem with one another...if one gets too powerful, than the country runs into trouble, but as long as they operate on equal footing we are okay.
I think there is a lot of rhetoric, but no where near along the lines of civil war. While there are a lot of ethical issues...I see none so powerful as slavery was, that is shared by an overwhelming majority on either side. The only thing I would ever worry about leading to a seperation of the union, would be a constitutional controversy over election voting procedures. If there were to be a flaw in the constitution....(which would be hard to find...it is an AWESOME document!), it is our voting procedures. Still, I have hope that the loser would have the common decency, such as Al Gore and others in his position, to lay down their challenges before they lead to a government crisis.
And if a crisis were to occur...Lord help us because I don't any of these men have the caliber of Lincoln, and even he needed a lot of backbone to hold things together.