Once upon a time Democrats were the opponents of Republicans. During that time they were able to work together to achieve certain important things for the good of the country.
Then Newt Gingrich (I have heard) decided to make the Democrats THE ENEMY and so decade after decade it has taken root and here we are today. Every change dd gets he attacks Dems as if they were the enemy as well as praising and complimenting a country that used to really be the enemy. Russia.
Now dd did not do this overnight of singlehandedly. He rode the coattails of those who came before and just exacerbated it and made way bigger and huger and importanter.
There was no one in the Republican camp to say "no that is not right". So here we are in a place that some love and some don't. If Newt never existed would someone else have initiated the same thing? Make an enemy out of your opponent and no holds are barred?