At a protest in Louisville, Kentucky, last month – the city where Breonna Taylor was murdered by police on 13 March – Chanelle Helm, a leading organiser in the local Black Lives Matter group, turned to the white protesters with a loudhailer. ‘If you are going to be here,’ she said, ‘you should defend this space.’

The white protesters – most of them women – linked arms and formed a line between the black protestors and the police. Tim Druck, a local photographer, took a picture. It went viral after the Kentucky National Organisation for Women and other groups shared it on social media.

Another tweet that went viral at the end of May was by Virgil Cent:

I think the craziest thing I witnessed today on the frontlines was Black People yelling ‘White Shield’ when the police were blocking and pushing us back

The white people moved to the front and protected us + the cops became less violent like wow wtf

However much the media and public officials love to describe contemporary events – whatever they may be – as ‘unprecedented’, when it comes to protest in America there is exactly one precedent: the civil rights movement. That has proven true yet again this week.

When my son, who’s 19, called from Minneapolis on Saturday night, I was watching the livestream of protesters defying curfew there for the second night in a row, and listening to young people dry heave, like my students in Colombia, from the tear gas. Because he has first-aid training for mountaineering, my son was volunteering in a medical tent clearly identified with a red cross, but the state police fired on them with tear-gas canisters and rubber bullets, and he and his friends hoofed it home. The real medics told him to stay in for the night. It was going to get rough.