Calculations about how the killing of George Floyd will affect the 2020 US presidential election will seem coldly rational — even offensive — to the thousands of protesters who have taken to the streets of America.

They, and many others, are haunted by the appalling footage of his dying moments, as he choked to death under a policeman’s knee. The protesters know that the US has a history of racial violence that goes back centuries. Even two terms in office for Barack Obama, the first ever African-American president, did not lead to the profound changes in race relations that many had hoped for.

The Black Lives Matter movement was actually founded during the Obama presidency — after the acquittal in 2013 of George Zimmerman, who was accused of the murder of Trayvon Martin, an unarmed black teenager. It gathered further momentum in 2014 — still during the Obama presidency — after the deaths of two more African-Americans, Eric Garner and Michael Brown, at the hands of the police. An academic study last year suggested that, over the course of a lifetime, black men in America have a one in 1,000 chance of being killed by the police, and are two-and-a-half times more likely to die this way than white men. African-Americans represent 12 per cent of the US population, but 33 per cent of the prison population. They are also dying in disproportionate numbers from coronavirus.