As reports began to appear of the disturbed background of Aaron Alexis, the media seems to have universally decided that mass shootings are readily explained by severe mental illness. The assumption is that as psychiatric disorder is so obviously linked to violence, there should be no surprise that the Washington Naval Yard killings involved someone with a mentally troubled history.

America's problem isn't its gun culture; America's problem is the mass psychosis which feeds its gun culture and fuels not just the normalisation of gun violence, but exalts it as the sine qua non of the strength and self assertion that informs the nation's identity.

Barack Obama finds himself in his second term of office, with no possibility of a third. If he wants to be remembered for anything more than being the first black man in the White House, this could be his Abraham Lincoln moment.

There are many who will be furious at the attempt to diagnose mass killers, believing this is a way of them 'getting off' or of eluding responsibility. But since the vast majority of those diagnosed with any psychiatric disorder are not violent, personal responsibility probably still has a role to play, even if psychotic processes can be found in these killers.