Gabrielle Giffords is the victim of a debased political culture

(AP)

One could be shocked, but hardly surprised, by the news that on Saturday morning the Arizona congresswoman, Gabrielle Giffords, had been shot while meeting with her constituents outside a Safeway supermarket in suburban Tucson, and that the gunman had killed six of the people who were with her, including a federal judge and a nine-year-old girl. It was an event that seemed to grow out of America's present disturbed and angry climate, like a killer-tornado or hurricane: awful, yes, but part of the weather, and, in some sense, only to be expected.

Within a very few minutes of the shooting, bloggers and Tweeters were putting out links to an ad published last March by Sarah Palin's political action committee, which showed a map of the United States, dotted with 20 vulnerable Democratic seats in Congress, each identified by cross-hairs in a gunsight. Giffords's seat, in Arizona's 8th District, was one of these. The legend above the map read: "We've diagnosed the problem... Help us prescribe the solution."

It would be absurd now to claim that the proposed "solution" was death by assassination. The gunsights were intended as an eye-catching metaphor in the metaphor-stuffed rhetoric of the Tea Party movement, which loves to harp on a fanciful parallel between today's opposition to healthcare reform, the stimulus package and the bank bailouts, the case for providing amnesty to illegal immigrants, and all the rest, with the great patriotic war of the American Revolution in the 1770s. It's the sort of historical comparison designed to appeal deeply to people who are ignorant of history, and it generates a stream of metaphors for heroic resistance, involving muskets, funny trousers and tricorn hats.

But Gabrielle Giffords made great sense when, in March 2010, she discussed the Palin map with a TV interviewer, saying: "Sarah Palin has the cross-hairs of a gunsight over our district – and when people do that, they've got to realise there are consequences to that action." In the martial atmosphere of an election year (and in a country where four sitting presidents have been assassinated, and many more have survived serious attempts on their lives), extravagant figures of speech can all too easily become literal, and rhetorical guns turn into real ones.

In November last year, Giffords was narrowly re-elected against a Tea Party Republican named Jesse Kelly, who, as a 6ft 8in former sergeant in the US Marine Corps, found it natural to conduct his political campaign in the language of warfare. Kelly called Palin "too moderate", and one can catch the flavour of his candidacy in this unpunctuated announcement of an event held on 12 June 2010: "Get on Target for Victory in November Help remove Gabrielle Giffords from office Shoot a fully automated M-16 with Jesse Kelly."

Kelly's campaign website closed down some time after noon on Saturday, and was replaced with a message of sympathy for Gabrielle Giffords and her family, along with the sentiment that "senseless acts of violence such as this have absolutely no place in American politics". Before the site closed, I caught his November thanks to the "thousands of warriors who fought with me in this campaign".

Given Kelly's background, one can see how voters became "warriors", fellow-infantrymen in the electoral battle, but the word also exactly reflects the Tea Party mindset: this is war. Or, as Sarah Palin put it in a Tweet last year: "Commonsense Conservatives & lovers of America: 'Don't retreat – instead RELOAD!' Pls see my Facebook page."

The Tucson shootings can't be blamed on Palin, Kelly, or the Tea Party: all three are more or less typical inhabitants of the debased, exaggerated and vitriolic language that now dominates American public discourse. Keith Olbermann, on the liberal left, speaks it as fluently as do Rush Limbaugh and Glenn Beck on the right.

The language was spawned on talk radio, where outrageous metaphors and wild logic flourish best, and where listeners, sitting alone in cars and trucks, can cheer on their favourite ranter, who is half improvisatory comedian, half Job the prophet. Every day of the week opens a new front in the war, as the loudmouth stars deliver their tirades, politicians copy them in both houses of Congress, and people at home grow used to the idea that political debates ought to be judged by the degree of overstatement and malignant rage deployed on both sides.

Before he took his Glock handgun to the Safeway parking lot on Saturday, Jared Loughner (b. 1988) had been setting himself up as a political commentator, posting videos on YouTube in which he displayed the texts of his homilies as white words on a black screen, printed in small blocks against a big background, as if they carried scriptural weight: "... I can't trust the current government because of the ratifications: The government is implying mind control and brainwash on the people by controlling grammar..."

Rich in malapropisms, barely literate, and impenetrably confused, Loughner's pensées convey a primitive, superstitious reverence for the printed word. That he doesn't appear in person on his videos suggests a mind enthralled by the power of language disembodied from any particular speaker, coming to us as if from an oracular cloud.

Loughner seems to be an uncomfortably familiar figure; one of those juvenile megalomaniacs with guns, who show up in the news at least once a year for having carried out a mass shooting at a US high school or college, nearly always remembered, as Loughner has been, as "quiet" and "shy". This time, though, the shooter entered the hyperbolic culture of American politics, where his action appears to fit almost seamlessly with the prevailing rhetoric of the day.

There is a chance, if rather a slim one, that the Tucson massacre will make both politicians and commentators draw back and reconsider their terms. Politics is not warfare. The Democratic party is not a colonialist tyranny. Obama is not George III. To live in a slew of overheated metaphors, in language vastly disproportionate to the occasion, is to invite and license the kind of atrocity that happened the day before yesterday.

Jonathan Raban's books include 'My Holy War: Dispatches from the Home Front', a collection of essays covering America in the George W Bush era; his most recent book, 'Driving Home: An American Scrapbook', was published last year by Picador