Protesters in front of Los Angeles City Hall last week. (Philip Cheung for The Washington Post)

The three words were once a controversial rallying cry against racial profiling and police violence. Now, “Black lives matter” is painted in bright yellow letters on the road to the White House. Celebrities and chief executives are embracing it. Even Sen. Mitt Romney, a Republican former presidential candidate, posted the phrase on Twitter.

As consensus grows about the existence of systemic racism in American policing and other facets of American life, longtime organizers of the Black Lives Matter movement are trying to extend its momentum beyond the popularization of a phrase. Activists sense a once-in-a-generation opportunity to demand policy changes that once seemed far-fetched, including sharp cuts to police budgets in favor of social programs, and greater accountability for officers who kill residents.

“It’s now something where the Mitt Romneys of the world can join in, and that was something unimaginable back in 2014. That is the result of six years of hard work by people who are in the movement and have put forward so many discussions that really changed people’s hearts and minds,” said Justin Hansford, who was an activist in Ferguson, Mo., during the unrest after the police killing of an unarmed black teen there. He is now the executive director of the Thurgood Marshall Civil Rights Center at Howard University.

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But activists’ demands to “defund” police departments have already become a point of division politically, with some prominent people who have expressed support for the movement — such as Romney (Utah) — saying they do not support what they see as an extreme policy position. President Trump has already suggested that his presumed Democratic opponent, former vice president Joe Biden, would be forced to cut funding to police under pressure from the left, even though Biden has also said he does not support defunding the police.

Where the conversation lands will be a test of just how mainstream Black Lives Matter has become.

The movement was sparked by the death of Trayvon Martin at the hands of a neighborhood-watch volunteer in Florida in 2012 and coalesced two years later amid demonstrations over the death of Ferguson 18-year-old Michael Brown, who was fatally shot by a white police officer. The protests drew an aggressive ­response by law enforcement, which stunned and radicalized a generation of activists.

Since then, the deaths of unarmed African Americans at the hands of police have become a mainstay of news coverage. And the developments of recent weeks show how the movement has embedded in the mainstream in ways that would have been unthinkable just a few years ago.

Americans have turned out for what researchers are calling the most sweeping and sustained protests in the country’s history, with demonstrations in all 50 states and the District of Columbia over two weeks. Corporate giants such as Walmart have added messages pledging a commitment to racial equality to their websites.

Last week, National Football League Commissioner Roger Goodell said that “we were wrong for not listening” to players who peacefully protested police brutality “and encourage all to speak out and peacefully protest.” He has not clarified what that might mean for athletes who kneel during the national anthem at football games, or for Colin Kaepernick, the quarterback most closely associated with the gesture, who was ostracized by the league for protesting police brutality.

A Washington Post-Schar School poll released Tuesday found that 69 percent of Americans say the death of George Floyd in the custody of Minneapolis police last month reflects a broader problem in the way black people are treated by police, compared with 29 percent who say it was an isolated incident. It reflects a striking shift in public opinion since 2014, after Brown’s death, when a Post-ABC News poll found that 43 percent of Americans believed recent high-profile police shootings reflected a broader problem and that 51 percent said they were isolated incidents.

And the current protests appear to have bipartisan support — 87 percent of Democrats, 76 percent of independents and 53 percent of Republicans say they support the demonstrations today, according to the Post-Schar School poll.

“Seven years ago, people thought that Black Lives Matter was a radical idea,” Alicia Garza, the co-founder of the Movement for Black Lives, told Chuck Todd on NBC’s “Meet the Press” on Sunday. “And yet Black Lives Matter is now a household name and it’s something being discussed across kitchen tables all over the world.”

It did not always seem likely — or even possible — that the American public would reach such an agreement about the role of racism in policing.

There was a time when it seemed to Dominique Alexander, an activist in Dallas, that the Black Lives Matter movement might collapse under the weight of scrutiny about the tone of its message and accusations about “reverse racism” against white people — accusations its organizers strongly rejected.

Alexander recalled the rally he organized in Dallas during the summer of 2016 to protest the deaths of two black men — Philando Castile in Minnesota and Alton Sterling in Louisiana — who were fatally shot by police. That day, a sniper who was not affiliated with the protesters killed five Dallas police officers.

Critics pounced, amplifying long-running accusations that the movement’s organizers encouraged anti-police violence. Black Lives Matter was intentionally a decentralized and diffuse movement that came together on the principle of the phrase itself. Still, activist leaders throughout the country had to figure out how to address the issue. Most asserted that the movement was against violence and in support of life — Alexander’s group held a prayer vigil for the slain officers the following week. Only 100 people showed up, a mere fraction of the numbers a week before.

“That next year was a struggling year, because people got scared with all the rhetoric going on against us,” Alexander said. “But we needed to keep going, and then people realized we were going to have another hashtag, another person that was killed [by the police], and another one, and that brings us to right now.”

The tenor of public discussions about race and racism in the United States changed dramatically later that year, amid a presidential election in which race relations had become a central theme. Alexander and others say Trump’s election prompted a larger, more diverse group of Americans to back the movement.

More recently, at a time of already heightened tensions because of the coronavirus pandemic, Floyd’s death unleashed a flood of energy and frustration over the direction of the country.

Jade Ashford, a 24-year-old college student from suburban Maryland who recently attended a protest in Washington, said she recalled anguished family discussions about race after Martin’s killing in Sanford, Fla., in 2012. But it was not until last month, when video of Floyd began to circulate, that she decided she wanted to participate in the protests.

“I felt like when we had the Obama era, things were getting better,” said Ashford, who is black. “But then I realized we had this whole other side of America who didn’t look like me or like me for wanting to speak up.”

Veteran activists across the country have made a similar observation — that Trump, who was not yet in office when Black Lives Matter activists began to organize, has brought attention to racism in the United States among white people who dislike the president.

“I think a lot of the Black Lives Matter movement’s rhetoric about how pervasive racism was in America seemed far-fetched to many people,” Hansford said. “But what our expectations are and what our norms are about race, all of that has changed because of Donald Trump and his election.”

Trump, who famously said there were “very fine people on both sides” at a white-supremacist demonstration and counterdemonstration in Charlottesville in 2017 has tried to combat perceptions that he is racist by touting the strong pre-pandemic economy, which he said benefited African Americans, and his signing of a criminal justice reform bill.

The current protests are happening against the backdrop of a global pandemic that, in the United States, has disproportionately hurt minorities. The crisis has helped call attention to the persistent resource gaps in black communities, said Jason Purnell, a public health expert in St. Louis, including insufficient access to health care and high rates of poverty.

That, in turn, has forced fresh questions about where government dollars are allocated and what share of that money goes to police departments compared with other spending priorities such as mental health care and education.

“We’re quite frankly expecting police to stand in for behavioral health systems that we haven’t fully funded and equipped, to stand in for social services and social work functions. But the police themselves will tell you that they don’t feel equipped to deal with that,” Purnell said. “We punish people for having problems rather than helping to address the problems that people have.”

Thenjiwe McHarris, a strategist in the Movement for Black Lives, the coalition formed by the three women who coined the phrase “Black lives matter,” said much of the movement’s work has happened away from well-covered protests and speeches.

Activists across the country have developed relationships with state and local leaders while lobbying for governments to spend less on policing and more on housing, mental health and social work. These efforts have resulted in drug intervention programs in the District and the dispatching of social workers to 911 calls in Dallas, McHarris said.

Some of the activists who rose to prominence in Ferguson have become regulars on cable television and maintain large followings on social media. Others have joined academia, where they help shape discourse on a variety of social issues.

Chelsea Fuller, spokeswoman for the Movement for Black Lives, said the movement’s core idea — that black lives are valuable — has benefited from its embrace in popular culture, particularly the “unapologetically black” aesthetic, which merged black history and civil rights causes with fashion and art. It seeped into Hollywood with shows such as “Black-ish,” and Ava DuVernay’s film “13th” and “When They See Us” series, which highlight the consequences of structural racism.

McHarris said that she is pleased to see the movement broadening but that it is “meaningless and harmful” when people join marches and post “Black Lives Matter” but do not advocate for substantive changes in policy.

One growing point of contention are the calls on the left to “defund the police,” a shorthand for redirecting police budgets to social service programs and other community infrastructure.

“It would be nuts to think we’re going to reduce our commitment to the police,” Romney told reporters Monday evening, referring to calls to slash police budgets. “At the same time, finding ways to reduce a bias that may exist on the part of individual officers or to reduce systemic racism, those are high priorities, and it should be aggressively considered and pursued.”

On Monday, Biden’s campaign put out a statement that the candidate believes police departments need additional funding to help diversify their workforces and to invest more heavily in body cameras.

“Vice President Biden does not believe that police should be defunded,” said Andrew Bates, a spokesman for the campaign. “He hears and shares the deep grief and frustration of those calling out for change, and is driven to ensure that justice is done and that we put a stop to this terrible pain.”

Scott Clement, Emily Guskin, Jessica Contrera, Peter Jamison and Kyle Swenson contributed to this report.