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.
All your examples are correct. But they are just examples of normal bare-knuckles infighting. Liberals were nasty to Nixon. But they never called him a Nazi. And liberals made fun of Ford. But they never called him a racist.
We are seeing a demonization of conservatives today that is unprecedented.
Back in the 1970s (I’m probably older than you!) I went to hear G. Gordon Liddy speak at a local public university. No one tried to shout him down. And no one was protesting outside.
No way would someone like Liddy be able to speak there today.