Enthusiastic, even vigorously insulting, exchanges between people of differing political views has been pretty much the norm for much of the nhistory opf the Republic. Just look at old newspapers; today's political vitriol often seems tame by comparison.
What's changed is that our society as a whole has lost certain extremely important concepts, concepts which ultimately boil down to the principle of self-ownership.
The specific concepts are honor, integrity, mutual respect, and humility. Guided by those, our forefathers could rail, insult, slur, fling mud, all just as we do, but at the end of it they still understood that the other guy is their fellow American, their fellow human being, their brother in this little adventure called life. Those are why a tycoon could stand on the street corner and talk to a bum, knowing deep inside that they two were equals, why everyone important treated everyone as a colleague.
We've lost that. When the American Dream was understood to be liberty, it was plain to everyone that "all men are created equal", that Jefferson's proposition wasn't something stuffed in a courtroom to keep things balanced, but a foundation for everyday life, it was obvious as water flowing downhill that before and above anything else, we were all partners, all here to stand together and help each other. So the words that politicians mouth today for form were actually meant; they considered one another colleagues first, and members of opposition parties second; they understood themselves as colleagues not because they'd been elected to the same governmental body, but because they were Americans.
The American Dream got changed from liberty to prosperity. The old "car in every garage" line had a lot to do with that; it put wealth above others, above country, above liberty. It made getting, and having, and winning more important than anything else -- and in so doing, it made people regard one another not as comrades in guarding liberty and thus each other, but as property, as targets of a battle in which the winner got to tell the loser how to live.
With stakes like that, civility goes out the window because of the larceny resident in every human heart, but at a deeper level because we have ceased to regard one another as equal.