As Trump Derangement Syndrome flourishes and drives Democrat politicians crazy enough to endorse open borders via the closing of the agency that protects them, and drives media figures to levels of on-air profanity that would have been firing offenses not long ago, it is easy to assume that things have never been this bad.  Andrew Malcolm, writing for McClatchy, provides some historical perspective, recalling some incidents that he personally witnessed during the Vietnam turmoil:

The retired Supreme Court justice acknowledged the banquet luncheon's standing ovation before beginning his remarks.  But shouting demonstrators burst through the ballroom doors.  Swinging car antennas like whips to ward off security, they jumped on the head table, kicked anything in sight, threw blood on dignitaries and lobbed a pig's head at the former justice.

Across town soon after, a female audience member at a public Board of Education meeting disagreed with a rabbi's testimony.  She swung a glass water pitcher and opened his skull.

He adds:

Most Americans weren't born by 1969, when those two opening incidents were personally witnessed.  So, they think today's civic rudeness is unprecedented.

It's not.

The contemporary hand-wringing over rude Americans being rude some more is almost laughable.  Asking someone to leave an obscure restaurant over distaste for their employer pales to insignificance when compared to the national divisiveness of, say, 1964-74.

I, too, lived through those years as a sentient adult, and I would add that there was a wave of terror bombings, bank robberies, and other lethal political violence.  Bad as the attempted mass assassination of Republican lawmakers on a baseball diamond was, I think the death toll attributable to Trump Derangement Syndrome so far is less than that of the much longer Vietnam era.  Thank God.

I'd add that if one goes back farther, we see much worse political violence, including the Draft Riots of 1863 in New York City that ended up with blacks being lynched, requiring President Lincoln to divert troops from the Battle of Gettysburg to control the violence.

New York Draft Riot (source).

But that was during an actual civil war, which broke out after years of agitation and violence over slavery – whereas we fear a second civil war after less than two years of agitation and some violence.

However, two factors are present today that are "rubbing raw the wounds" (Alinsky's expression) unlike in the past.

One is social media that allow people to organize instantly on the basis of a shared passion.  This is a danger whose full impact is yet to be realized.  Get one percent of the population angry enough to riot, and in a city of a million, that can turn out 10,000 violent rioters.

A second factor distinguishes our era from that of the Vietnam turmoil: a fractured media that features outlets catering to minority passions.  Back in the Vietnam angry years, there were three television networks, all dependent on federal licensing, and everywhere but a few cities, monopoly local newspapers, all of which saw the need to avoid alienating the political center.  That's why the era led to the rise of "alternative" weekly newspapers like the Boston Phoenix, catering to alienated young adults and adolescents.

But in the era of internet media dominance, virtually any and every niche has multiple publications, and they compete for attention by metaphorically yelling louder.  

I think Andrew Malcolm has provided necessary perspective, but I'd add that we are barely a year and a half into the era of Trump.  My fears are of political assassinations and riots getting much worse, egged on by social media and the spread of actual derangement.