Jack - "It will only end if one of the Parties abandons the fringes and governs for the 60-70% of the population in the middle."

Agreed, Jack. That would end it. But I see no real sign of either of the Parties doing that. Instead, they are doing what profits them most in the very short run, and instead of serving the 60-70% of the population in the middle, they are provoking and manipulating the extreme fringes and serving the wealthy elite.

What motivation do they have to stop doing that under the present system?

Sanity? A sense of social responsibility? Love of their fellow humanity? Moral idealism?

Apparently none of those have proven to be a strong enough motivation thus far...in the face of the following 2 dominating motivations:

Profit and Power.

*****

The 60-70% of the population in the middle could force them to do it. That would require a second American Revolution.