The crisis cascading through American cities has allowed voters to make real-time comparisons of two presidential candidates' leadership styles.
It's been instructive.
Donald Trump and Joe Biden have responded to civil unrest by revealing different behaviours, priorities and ideas about government itself.
The current president called for the military. Biden called for social change.
The presumptive Democratic presidential nominee forecast a years-long battle ahead against racial disparities in health care, economics and policing.
"A wake-up call for our nation. For all of us," is how Biden described the killing of George Floyd in Minneapolis, Minn., which triggered a wave of protests across the country, as well as a third-degree murder charge against the police officer who kept his knee pressed on Floyd's neck for nearly nine minutes.
"It is the work of a generation," Biden said of the task facing the country.
Trump demanded a swift restoration of stability.
He has prefaced his public remarks by expressing sympathy for Floyd, and for peaceful protesters.
He has also referred to his administration as the best for black Americans since Abraham Lincoln ended slavery (he tweeted about low unemployment, reduced criminal sentences, and new tax incentives for businesses).
But that's not his main message on the current crisis.
The message that dominated Trump's public speeches and social media feeds was to threaten military action against "thugs … violent mobs, arsonists, looters, criminals, rioters, Antifa."
A revealing word count
One way to gauge their contrasting priorities is simply by counting the sentences in their speeches — the number devoted to quelling violent protests versus the number expressing sympathy for protesters' concerns.
Trump's last two significant public statements, over the weekend and on Monday, included twice as many, then about 20 times as many, sentences about restoring order.
WATCH | Trump threatens to use the military against violent protesters:
A Biden speech Tuesday in Philadelphia featured the opposite: he briefly condemned looting, then spoke about 30 times more about protesters' concerns.
It's a relatively rare natural experiment for voters to observe candidates in a real pressure-cooker setting relevant to the actual job of being president.
What often happens in a presidential campaign is, at best, loosely connected to the task of leading the U.S. executive branch.
Candidates will offer 10-point plans for this or that proposed law, but details of a law are really up to Congress.
Obamacare is a classic example of this. What Barack Obama proposed as a candidate for health reform, and what Congress eventually passed during his presidency, were very different.
A test involving what presidents actually do
But this crisis has brought into relief two important parts of a president's job — in fact, they are two of the most important parts of the job, along with international relations, leading the military, and instructing the bureaucracy.
One job is running the Justice Department.
The other is setting the tone of a national conversation — using what President Teddy Roosevelt called the bully pulpit.
WATCH l Biden accuses Trump of divisiveness:
Biden referred to it several times in his speech Tuesday. He called for an era of action to reverse systemic racism, with long overdue and concrete changes.
Trump's national security adviser, Robert O'Brien, denied last weekend the idea that systemic racism exists in U.S. police forces.
More government or less
Biden had made clear he sees a larger role for government in health care, and mentioned it Tuesday in the context of racial justice.
He noted the higher rates of illness and death from COVID-19 in black communities. He said he wants to expand U.S. health insurance programs to cover more people, and that he would roll out new economic proposals soon.
A Trump White House policy adviser also said a series of economic announcements is coming. She talked about the importance of deregulation.
"Moving government out of the way," is how Brooke Rollins described it in a panel interview Monday with Politico.
She said, for example, that a single mother in Detroit who wants to start a hair salon has too many rules to follow.
She and Trump in recent days have also referred to his policy of supporting charter schools, to offer alternatives to under-performing public schools.
Criticism of police
Biden made police reform a significant part of his speech Tuesday. He called for Congress to pass a bill outlawing chokeholds; an end to transferring military equipment to police forces; a new national police oversight commission; and a review of training and de-escalation practices.
Trump, who has previously joked about and encouraged police use of force, has been more circumspect.
He called Floyd's death a tragedy that should never have happened and said his administration had opened a civil rights investigation.
When it comes to controlling protests, Trump has used tougher language, matching his harder-line policy.
He's called for governors to deploy the National Guard to control unruly crowds. He has tweeted about "vicious dogs" and "ominous weapons" waiting for protesters who breach the White House grounds.
Biden ridiculed that talk Tuesday. He said the president should be reading the Bible instead of posing with it in pictures, and also suggested he read the U.S. Constitution, to learn about love, tolerance and freedom of assembly.
"That's hard work. But it's the work of America," Biden said.
He was referring to a Trump photo op this week that involved forcefully clearing protesters from an area outside the White House so the president could cross the street and stand outside a church, whose office had been burned during a protest, while holding up a Bible.
One other obvious difference on display Tuesday involved the pandemic, which has killed more than 106,000 people in the U.S.
As he arrived to speak at a podium, Biden pulled off a face mask, which he's been wearing in public during the health scare.
Trump has avoided being photographed wearing one.
How it plays out politically
So, how will all this play out in the November election? It's too early to say. There isn't much polling since the protests broke out, and one new survey had some mixed findings.
Trump might appreciate some results of a Morning Consult poll of 1,624 voters, conducted between May 31 and June 1. A majority of respondents supported the idea of calling in the military — 58 per cent favoured it, while 30 per cent opposed it. A smaller plurality also supported how police have handled the protests.
Yet there are warning signs for Trump, already behind in most national polls.
Respondents gave Biden higher marks on race issues (47 per cent favoured Biden, 30 per cent Trump), and a clear majority said they also supported the protests (57 per cent to 23 per cent opposed).
Their overall conclusion? When asked if recent events made them likelier to support one candidate or the other, respondents, by a margin of 12 percentage points, answered Biden.