Jo Cox, the Labour MP for Batley and Spen, was killed yesterday outside her constituency surgery in Birstall, West Yorkshire. The circumstances alone are shocking, but the details make it more unbearable: a former head of policy at Oxfam, she had fought for years on maternal mortality, and supported Alf Dubs’s amendment to the Immigration Bill that would have allowed 3000 unaccompanied child refugees into the country; she was a young and newly elected MP; she was the mother of two small children, who will grow up without her; she was killed after sitting in a library waiting for constituents to tell her their problems. Her death comes during a poisonous referendum campaign that has focused on race and nationalism, and the person accused of stabbing and shooting her has reportedly had links with far-right white supremacist groups. According to witnesses he shouted 'Britain first' during the attack.

Hate is an easy emotion to provoke but a difficult one to control. For years, political parties and movements have sought not to quell but to harness it. The referendum campaign has been toxic, focusing less on what Britain's membership of the EU actually entails than on immigration and, in turn, migrants. This may be the logical end point of a rhetoric that whips up hatred: a murder on the street in the name of nationalism.

The far-right organisation Britain First – it calls itself a 'patriotic political party and street defence organisation' – sought to distance itself from the killing. Earlier this week, it was reported that the group had held a training camp in Snowdonia, teaching martial arts and ‘knife defence’ to its members.

The political environment has grown more heated with the referendum campaign, but there's nothing new about the rhetoric that hones in on 'immigration', fostering antipathy towards anyone who isn't white or was born outside the UK. The Conservatives’ 2005 campaign poster 'It’s not racist to impose limits on immigration,' scrawled on a white background in childish handwriting, dovetails with Labour’s 2015 'Controls on Immigration' mug, a message the party felt both important and profitable enough to put on its campaign merchandise. The Islamophobic Tory campaign against Sadiq Khan in the London mayoral election was seen as politically palatable in the scrum for votes.

For years, politicians have sought to assuage racist views by arguing that it isn't racist to be concerned about immigration, couching anti-immigration sentiment in vague economic concerns about ‘stolen’ jobs, but it often is straightforwardly racist. Pandering to racism and fascism emboldens these beliefs: tolerating the far right in a misguided attempt to shore up votes does nothing of the sort, but normalises hatred instead. Nigel Farage said on the BBC last month that 'if people feel that voting doesn’t change anything, then violence is the next step.'

There will always be a topical reason for politicians to claim that racism should be understood: the extension of the Eurozone and free movement, the recession, the housing crisis, the refugee crisis. At what point will they stand up and try to combat the racism endemic in British society, rather than softly align themselves with it? If politicians and the media tell people their 'way of life is under threat’ often enough, people will believe them. Politicians and the media aren’t responsible for Cox's death, but they are responsible for creating a toxic climate in which hatred has won out and is deemed an acceptable response to anger.

As with the massacre in Orlando, which some people tried to deny was a homophobic, politically motivated attack, politicians and commentators will claim that links cannot be drawn between the killer's motives and the political climate. Thomas Mair, the 52-year-old local man arrested after the attack on Cox, reportedly had mental health problems. But most people with mental health problems are non-violent, and people with mental health problems, like everyone else, do not live in a vacuum. We are constantly fed a message that racism is not to be deplored but understood; hatred is pandered to and used for electoral gain. Cox’s husband said in a statement yesterday that 'she would have wanted two things above all else to happen now, one that our precious children are bathed in love and two, that we all unite to fight against the hatred that killed her.'