Leading article: The fruits of political extremism

The motives of the gunman who shot the US Congresswoman Gabrielle Giffords and killed six bystanders in Tuscon on Saturday are unclear. We do not know whether the youth who has been arrested for the crime, Jared Loughner, was driven by political grievance or mental illness. But to many in America this looks like an atrocity that was waiting to happen.

Since Barack Obama entered the White House two years ago, the American right has adopted partisan rhetoric of the most reckless kind. A year ago, Sharron Angle, the right-wing Tea Party favourite and Nevada's Republican Senate nominee, warned that "if this Congress keeps going the way it is, people are really looking toward those Second Amendment remedies". This was a reference to the right of US citizens to bear arms. Meanwhile, the former Republican vice-presidential candidate, Sarah Palin, has sought to motivate supporters with slogans such as "Don't retreat – instead, reload".

The vitriol has been alarmingly personal too. President Obama has seen his place of birth and religion repeatedly questioned by right-wing "shock jocks" and political opponents alike. And Ms Palin featured Ms Giffords, along with 19 other Democratic Congressional Representatives, on an electoral "hit-list". The Congresswoman explicitly warned about the use of rifle cross-hairs on Ms Palin's website, saying: "When people do that, they've got to realise that there are consequences to that action." Those words now look chillingly prescient.

We must await further information before drawing conclusions about what took place in Tuscon. But history teaches that in climates of political polarisation, spontaneous acts of political extremism are more likely to occur. And if politicians routinely use the language of violence, actual violence is more likely to break out.

President Obama has urged all Americans to "come together and support each other" in the wake of the shooting. No doubt they will do so. But what the US needs even more is for those who aspire to political leadership to at last start showing some responsibility.