[Buckeye McFrog]

When did it become acceptable for the two parties to just fight each other rather than actually govern from a “relatively common values system”.

When the Democrats abandoned that "relatively common values system". I would peg the date to sometime between the '68 Chicago Convention and the publication of Rules for Radicals.

[Mr. Douglas]

I think you are on to something. And to add my two cents, whenever that date happened, that was the beginning of the US becoming a “dead country walking.”