The parties used to work together, it was unthinkable to not compromise for their constituents. Today we hear politicians talk as if it would be treason to work with members from the other side.
There is no both sides in this either. One side wants to govern alone to their own interests, not those of their constituents.
Obviously there is more than just this, but Newt Gingrich has a lot to answer for
https://www.theatlantic.com/magazine/archive/2018/11/newt-gingrich-says-youre-welcome/570832/