America has been here before, split by racial division that left its cities in flames and its citizens demanding a different country.

But not for half a century, and never with a president whose response to demands for basic justice were so belligerent and divisive that even his former top military officials have turned on him.

By the end of the week, Donald Trump, who promised to build a “big, beautiful wall” to protect America, had thrown up a large steel fence around the White House as the sense of a presidency under siege grew.

The fires lit in Minneapolis by a police officer squeezing the life out of George Floyd, by kneeling on his neck for nearly nine minutes, ignited the biggest protests since the anti-Vietnam war and civil rights movement of the 1960s.

Most of the demonstrations were peaceful, and where they weren’t that was frequently down to the police. But rioters left a five-mile long scar through southern Minneapolis as they burned and looted their way along one of the area’s main shopping thoroughfares after ransacking the police station at the centre of the storm over Floyd’s death.

From there, a surge of anger radiated across the country, driven in good part by the nature of the nine-minute video of Floyd’s killing, but also the frustration that for all the promises made with each police killing of an unarmed black man they do not stop.

When the traumatic video of Floyd begging for his life met the tinder of weeks of coronavirus lockdown, surging unemployment, and a tanking economy the fire raced through America. It ignited protests and riots from New York to Los Angeles and the south, and then London, Berlin and beyond.

Now, as 50 years ago, the national guard were called out to face down the demonstrators, although this time it was also to stand guard over the violent dispersal of a legal and peaceful protest to provide a photo op for Trump. Now, as then, the president accused “outside agitators” – Trump called them terrorists – of stirring up trouble.

But this time, voices from the American establishment spoke up in support of those demands, and warned that the US is at an inflection point.

So, apparently, was Trump’s presidency, as he flailed while his tested tactic of divide-and-rule proved less effective. The power of the nearly nine minutes of Floyd’s suffering as the police officer charged with his murder, Derek Chauvin, looked into the camera was taken as a statement of police contempt for African American lives and the Black Lives Matter movement.

It was the moment when many of the doubters in America, the people always prepared to give the police the benefit of the doubt, were confronted with the indisputable evidence that police treat black people differently. If further evidence was required it came in the swirl of recordings of officers beating peaceful unarmed demonstrators that in some cities, including New York, drew accusations of a police riot.

By the end of the week, the entire culture and practice of policing in America was on trial and not just over Floyd. But it was more than just policing.

Tim Walz, the governor of Minnesota, where the protests began, described the uprising as a singular opportunity in his state’s history to break the chain of “systemic racism and the lack of accountability up and down our society that led to a daytime murder of a black man on a street in Minneapolis”.

“I think this is probably our last shot as a state and a nation to fix this systemic issue,” he said.

The Rev Al Sharpton, a central figure in America’s civil rights movement, put it more succinctly in a rallying cry at the Minneapolis memorial service for Floyd on Thursday. White America, he said, needed “to get off our neck”.

“The reason we could never be who we wanted and dreamed of being is you kept your knee on our neck,” he cried to shouts of agreement. “We could do whatever anyone else could do. But we couldn’t get your knee off our neck. What happened to Floyd happens every day in this country in education and health services and in every area of American life.

“It’s time for us to stand up in George’s name and say: get your knee off our necks.”

There were signs that the rest of America is ever more willing to hear that message than ever.

Almost no one was willing to try to defend Chauvin’s abuse of Floyd.

Whereas construction workers turned on the anti-war protesters who marched through New York after the national guard shot demonstrators at Kent State University in 1970, this week “hard hats” working in the city were seen clapping the demonstrators demanding justice.

As the police teargassed and shot at people protesting legally from Portland to Kansas City, those on the receiving end included Americans not usually found marching to demand police accountability. Even some Republicans normally quick to defend the police were alarmed enough by the video of Floyd’s death to turn out to march.

In many places, the violent police response to legitimate protest only strengthened the sense that the problem lies deep in the culture of militarised police departments that act like occupation forces in minority communities.

Yet there were also glimpses of progress. Police officers in other parts of the country – in Texas, Kentucky, Florida and other Trump states – went down on bended knee in a show of solidarity with the demands of demonstrators. Among them was the police chief of Ferguson, Missouri – the birthplace of the Black Lives Matters movement six years ago following riots and protests over the police killing of Michael Brown.

The president instinctively lashed out over a crisis he couldn’t control, with his tested attempts to create division and mayhem. But it proved to be the week when lines began to be drawn on the limits of Trump’s power to subvert.

The president has already neutralised the US justice department, freeing his allies from prison and compromising investigations. The supreme court is weighted in favour of his agenda, thanks to the highly politicised nomination process placing ideology over competenceunder a Republican-run Senate afraid of Trump.

That left the military as the remaining branch of government over which his malign influence was not yet decisive.

Then came what was quickly tagged the Battle of Lafayette Square, a small patch of park in front of the White House.

A large and noisy group of protesters had gathered there to make known their support for demands that all of the police officers involved in Floyd’s death be arrested. Ever sensitive to criticism, Trump was feeling humiliated by a report that he’d bolted for a bunker under the White House a few days previously when demonstrators tried to climb its fence.

Driven by his inner Putin, Trump decided to prove his courage by wading manfully into Lafayette Square to have his photo taken holding a Bible in front of a church. That would have the added benefit of playing to the evangelical vote.

But first the peaceful protesters had to be cleared. Trump’s attorney general, William Barr, ordered the police to empty the square, which they did with teargas and baton charges backed by soldiers of the national guard.

Not long after, the sight of the chairman of the joint chiefs of staff, Gen Mark Milley, in combat fatigues marching behind the president as he strode across Lafayette Square seemed to give a stamp of approval to Trump’s threat to turn out the military against those he was labelling domestic terrorists.

The president’s allies in Congress upped the ante, with Senator Tom Cotton proposing to send in the 82nd Airborne or “whatever it takes” against those he called “insurrectionists”. Trump, as ever on Twitter, gave that idea the thumbs up.

Faced with this, America’s military establishment chose a side.

The first to break cover was James Mattis, the marine general who resigned as Trump’s defence secretary in December 2018 and kept silent until now. He described himself “angry and appalled” at Trump’s response to the protests and called him as a threat to the constitution.

“Donald Trump is the first president in my lifetime who does not try to unite the American people – does not even pretend to try. Instead, he tries to divide us,” said Mattis.

Mattis’s specific point of contention was Trump’s use of the military to clear protesters “to provide a bizarre photo op for the elected commander-in-chief, with military leadership standing alongside”.

Admiral Mike Mullen, the former chairman of the joint chiefs of staff, said he was “sickened” to see the national guard and other security forces used to “forcibly and violently” clear a path for the president’s “stunt”. He accused Trump of disdain for the right of peaceful protest and said he was “deeply worried” that the military will be co-opted for political purposes.

“I have to date been reticent to speak out on issues surrounding President Trump’s leadership, but we are at an inflection point, and the events of the past few weeks have made it impossible to remain silent,” he said.

The head of the national guard, Gen Joseph Lengyel, felt it necessary to stake out a position just in case anyone thought he was siding with the president on the value of black lives. He said he was “sickened” by Floyd’s killing and “enraged” at the deaths of unarmed black men at the hands of “police brutality and extrajudicial violence”.

Esper retreated. On Wednesday, he disavowed the idea of sending the military in to control the streets of America’s cities. Not long after, the Pentagon began pulling out 1,600 troops moved to the Washington DC area during the protests. Few expect Esper to survive in his job for very much longer.

But the real damage was inflicted on Trump. His chaotic handling of Covid-19, with deaths close to 110,000 and rising, had already damaged his diminishing prospects for re-election.

The pandemic has also badly hit the one issue on which many Trump voters were prepared to forgive him all else: the economy. More than 20 million jobs were lost in April. May saw 2.5m of those return, although unemployment for African Americans kept rising.

Trump’s response to the employment numbers on Friday was to describe it as a “great day” for Floyd.

“Hopefully, George is looking down right now and saying, ‘This is a great thing happening for our country. A great day for him, a great day for everybody,” he said.

For his critics, the comment was another piece of the president’s casual callousness mixed with self-obsession. But for all his boasts, Trump can no longer make claims for a booming economy, even if stock market growth did not translate into better standards of living for most Americans.

“If 110,000 people have died and there’s been no response, if we can move the National Guard in a matter of hours but we can’t keep people safe from a pandemic, it goes to show what the priorities are,” said Annie Isler, a middle school teacher outside the Floyd’s memorial in Minneapolis.

Opinion polls put Joe Biden, now officially the Democratic nominee, ahead by 10 points or more.

Confronted with this on Fox News, Trump said that four years ago the polls said Hillary Clinton was going to win and they were wrong. In any case, he has his own numbers.

“I have other polls where I’m winning, and you’ve seen them, too, I guess,” he said.

No one else appeared to know where these polls were.

As Minneapolis picked up the pieces, Al Sharpton led the memorial service for George Floyd. Alongside his demand for white America to “get off our necks”, and the heart rending glimpses into Floyd’s life from his family, perhaps the most tortuous part for the mourners was when Sharpton asked them to stand in silence for eight minutes and 46 seconds to understand just how long Chauvin kept his knee pressing down on the African American man’s neck.

“As you go through these long eight minutes, think about what George was going through, laying there for those eight minutes, begging for his own life.We can’t keep living like this,” he said.

But Sharpton is a preacher, and he was not going to leave his audience without a brighter future to cling to.

“I’m more hopeful today than ever,” he told the mourners. “When I looked this time and saw marchers were in some cases young whites outnumbering the black marchers, I know that it is a different time and a different season.”

Sharpton described an incident at a civil rights march years ago and being confronted by a white woman who looked him in the face and said: “Nigger go home.”

This week he came face-to-face with a young white girl.

“I braced myself and she looked at me and said: no justice, no peace,” Sharpton recalled, to a roar of approval from the mourners.

“This is the time. We won’t stop. We’ll keep going until we change the whole system of justice.”