re: What changed political views and the animosity of parties so much in 2000?

I think a big part of the problem is the internet. The media has stopped doing it's jobs and is spending their time looking for clicks. So sensationalism is the key. They don't spend any time reporting on mundane, but important issues like the budget, infrastructure, campaign finance reform.

They spend all their time trying reporting on racism, homophobia, mass shootings, etc. This has stirred up the emotions of the electorate and people are being radicalized and argue everything at the extremes, which drives the anger.