You might be right. But until the presidency of Barack Obama, liberals and conservatives were at least civil to each other. That's all gone now.
Oh, and here's a photo of Reagan making Mondale laugh during a debate. Those were gentler, more civil times. Nobody called anyone else a "hater" or a "Nazi".
"I will not make age an issue of this campaign. I am not going to exploit, for political purposes, my opponent's youth and inexperience"
I will take back what I said. There was a second time when the country came together again, left and right, for a very brief moment. It occurred immediately after 9/11. That was something to see, and it did make me proud to be an American. But it didn't last very long.
So, no, I generally disagree with your premist that until Barack Obama that liberals and conservatives were at least civil to each other.