Fraud
"The Dallas, Texas, airwaves were particularly radioactive; preachers and political leaders and local businessmen spewed extremist vitriol on the city's radio and TV stations, inflaming the passions of the city's legions of unhinged fanatics. There was something about the city -- a rage or craziness, that, whether sensible or not, seemed to have set the stage for Jack's murder."
Just how ugly was the political atmosphere in Dallas? Kennedy turns to the late William Manchester, who described the city with, you know, great restraint and a care for fact:
"Huge billboards screamed 'Impeach Earl Warren.'" Jewish stores were smeared with crude swastikas. Fanatical young matrons swayed in public to the chant"Stevenson's going to die -- his heart will stop stop stop and he will burn burn burn!"
Try to put all of these images into being: the billboards that called for Warren's impeachment were"huge," and so apparently much larger than the city's regular billboards; they"screamed," which must have been disconcerting to passers-by;"Jewish stores" (whose mothers were presumably also Jewish stores) were"smeared" with" crude" swastikas, as opposed to the many apparently neat and precise swastikas used for other local purposes; and our"fanatical young matrons" no doubt struggled to get through their days as the spontaneous urge to sway and chant for the murder of Adlai Stevenson set upon them in grocery lines or behind the wheel of a car. There must have been traffic accidents, yeah? ("Daddy, why isn't mommy eating her dinner?""Kids, you know not to bother mommy while she's chanting and swaying. Eat your peas.")
This unhinged use of language reflects a larger and more unhinged rhetorical operation: Kennedy is making shit up. As a matter of historical fact, Dallas was unquestionably the site of significant far-right rage in 1963. But it's most unlikely that Lee Harvey Oswald, whose Soviet wife gave birth to their first child while the couple still lived in Minsk, was influenced by right-wing rhetoric.
Here is the Warren Commission's discussion of right-wing rhetoric in Dallas as an influence on Oswald. Here is the commission's discussion of their belief that Oswald had previously tried to murder a prominent Bircher. Here is their discussion of his life in the Soviet Union. Here is their discussion of his political views.
There's real far-right violence in our past. You can make arguments about its historical significance without resorting to plain invention.
Similarly, if you want to argue that right-wing rhetoric caused Jared Loughner to shoot Gabrielle Giffords, you have to show evidence to do it: a photograph or eyewitness statement that places him at a Tea Party event, a link to statements he made at a right-wing website, a description of his political views from friends, anything like that. To simply invent a political connection to an act of violence is disgraceful. Prove it, or don't do it.