I am certainly no historian, but I do pay attention to the current events that I consider to be impactful. With that said, I offer this concerning the current political divide in America.
In my estimation, the great divide we our witnessing today began to manifest itself in the 2000 Bush/Gore election. The Democrats were so angered over the loss of that election that, by my observation, they were scarcely ever able to get on board with Bush. Sure, 911 brought some working together, but legitimacy was never extended to Bush. Then, came Obama. Never have we seen a President so bent on undoing America, nor one who was so successful at it. The right was unable to accept him. Then, as far as the pendulum had swung to the left, it swung to the right with Donald Trump. Unless you are in a coma, you can see just how shamefully the left is rejecting him. It all started in earnest with the Gore loss.
The wrestling together and haggling that we see happening in the Republican Party right now is what we used to see happening between Democrats and Republicans. So, in effect, we have a three party system: the far left, and two wings of conservatives.