More than just the elites. The extreme division between all Americans from any group - political, racial, religious etc. - is all part of a large, ongoing cyberwarfare attack from Russia:

https://en.wikipedia.org/wiki/Internet_Research_Agency

I'm sure other nations are involved, Russia has just done the most recorded damage so far. The entire point of red vs blue, black vs white, rich vs poor rhetoric is to divide and conquer the American people.

There are possibly many entities with interests in destabilizing the US. The US does the same to other countries. I'm not talking about cyberattacks and the Russiagate hoax invented by the mainstream media in collusion with Hillary Clinton. I'm talking about the words and actions of the most powerful people in the world who are on all the big corporate boards and have the backing of every big media outlet. The Russiagate hoax deserves a thread of its own.

Income/wealth inequality, stagnating wages, regulatory capture, racial tensions and inequities, and deindustrialization, are absolutely real and a problem.

But yes, the divisiveness and corrosive, adversarial dynamics of the discussion around those issues is largely synthetic. And it's not just from other countries. A lot of American citizens that have power in the status quo would prefer if the status quo were not possible to productively challenge. And a lot of other American citizens that care about nothing simply don't mind fracturing and dismembering the discourse if doing so is the most convenient way to maximize paperclips— Uh, ad profits.