Amid the famous politicians, wealthy donors and top Democratic Party officials invited to New York last month to watch Hillary Rodham Clinton announce her candidacy for president sat another VIP guest — a newcomer to politics, but a man whose presence at the event was sought after by Clinton aides.

DeRay Mckesson, 30, one of the most visible organizers of the Black Lives Matter movement that has sprung up in the wake of the Ferguson, Mo., protests, had received a personal invitation to attend, and the campaign encouraged him to tweet his observations to his 178,000 followers.

He wasn’t impressed.

“I heard a lot of things. And nothing directly about black folk,” Mckesson wrote moments after the speech. “Coded language won’t cut it.”

Then this week, Clinton rivals Bernie Sanders and Martin O’Malley each began a frenetic push to appease Black Lives Matter activists angry at the way the two men handled a demonstration by the group at a liberal conference last weekend. O’Malley appeared on a black-oriented talk show to say he made a mistake, while Sanders called activists to request meetings.

The rise of Black Lives Matter has presented opportunities for Clinton and her opponents, who are seeking to energize black voters to build on the multiethnic coalitions that twice elected Barack Obama. But the candidates have struggled to tap into a movement that has proven itself to be unpredictable and fiercely independent. It is a largely organic web of young African American activists — many of them unbound by partisan allegiances and largely unaffiliated with establishment groups such as the NAACP that typically forge close ties with Democrats.The strained interactions demonstrate the extent to which a vibrant, new force on the left has disrupted traditional presidential politics, creating political challenges for Democratic candidates who are facing intense pressure to put police brutality and other race-related issues on the front burner for the 2016 election.

Led by several dozen core activists, many of whom voted for the first time in 2008, Black Lives Matter has organized protests at times drawing hundreds of participants that have occurred in more than two dozen cities and college campuses. Many of the movement’s leading activists are among Twitter’s most influential users — with the ability to pump messages out to hundreds of thousands of people, often prompting topics to trend nationwide. At times, they have pressured media outlets to cover stories surrounding race and justice, and have leveled sharp critiques of politicians and celebrities that often go viral — including negative comments about Clinton, Sanders and O’Malley.

The activists say they are now ready to have their say in the presidential race. While they are pressuring candidates to talk more about police brutality, they say they intend to carve out a broader agenda encompassing other issues relating to systemic racism.

“If you are running to be the leader of the free world it is your responsibility to seize the opportunity that the protest movement has created,” said Brittany Packnett, 30, a St. Louis-based activist who also serves on a White House task force formed after the Ferguson protests to study policing issues.

“Unless candidates are willing to discuss legislative, statutory and legal action that they will support or take themselves as president in order to right deeply-entrenched historical wrongs, then they’re not really ready to play at the level that the protest movement will require of them,” Packnett said.

Another leading organizer, Patrisse Cullors, added: “It’s not going to be easy to get our votes.”

“While it’s inconvenient, or it makes some people uncomfortable, we can’t go back,” said Donna Brazile, a Democratic strategist who has taken heat in recent weeks for defending Clinton against criticisms from some Black Lives Matter activists. “Politicians need to tune in.”Democratic leaders are taking note, say party strategists. The campaigns recognize the importance of reaching out to the movement, and understand the perils of ignoring it.

The activists made their biggest campaign splash yet last weekend in Phoenix, at the annual Netroots Nation conference in their surprise disruption of the joint appearance by Sanders, a Vermont senator, and O’Malley, the former Maryland governor.

Some activists had already begun to view Sanders and O’Malley with skepticism.

Some had expressed concern, for instance, that Sanders — whose elections in heavily white Vermont had not involved much outreach to black voters — was not talking about race in his presidential campaign.

And O’Malley had earned mixed reviews from a meeting a few days earlier in New York with more than a half dozen Black Lives Matter organizers. Several in attendance said he stuck to “talking points” and said he was not ready to talk specifics, though O’Malley’s deputy campaign manager, Karine Jean-Pierre, said he made it clear his goal was to “listen and hear what they had to say” and that he was “thinking through the policy.”

At Netroots Nation, the two candidates, who are attempting to challenge Clinton from the left, might have expected to receive a warm welcome. Instead, they seemed to wilt under the questions of protesters, who stormed the space around the stage and recited the names of blacks killed during confrontations with police.

The episode has been seen by many liberal activists as an embarrassment for the two candidates, who appeared surprisingly ill-prepared to respond to questions many thought they should have expected.

Sanders threatened to leave the stage as protesters demanded that he repeat the name of Sandra Bland, a black woman who died in a Texas jail cell earlier this month. Then he canceled a series of meetings he had scheduled with some of the activists following his appearance — something they found out only when campaign manager Jeff Weaver showed up in Sanders’s stead.

“I think they were trying to staunch the bleeding from the larger conversation about Sanders, that he’s not talking about issues of color in his stump speech,” said Elon James White, co-founder of a popular online broadcast, “This Week in Blackness.” “And then [they] canceled.”

O’Malley responded by telling the protesters, “Black lives matter. White lives matter. All lives matter” — a statement that struck the demonstrators as dismissive of their movement and the unique discrimination endured by African Americans at the hands of the police.

Within days of Netroots Nation, both candidates were scrambling to make amends.

Officials from the Sanders campaign called Cullors requesting a meeting to discuss policy issues.

Sanders used an appearance in Houston this week to discuss the Bland case, saying to thunderous applause that it is “unacceptable that police officers beat up people or kill people.” Then, late Tuesday night, after the release of video from the police’s confrontation with Bland, Sanders quickly released a stern condemnation, saying the video shows the need for “real police reform” and calling police abuse an “all-too-common occurrence for people of color.”

O’Malley took to the airwaves with a contrite appearance on “This Week in Blackness.”

“I meant no disrespect to the point, which I understand, and that Black Lives Matter is making,” O’Malley told host L. Joy Williams. “That was a mistake on my part.”

Some Republicans have seized on the movement’s disappointment with Democrats. In a July speech at the National Press Club, former Texas governor Rick Perry called on his party to admit that black Americans had been oppressed and sometimes left out of the economy. “It is Republicans, not Democrats, who are truly offering black Americans the hope of a better life for themselves and their children,” he said. Sen. Rand Paul (R-Ky.) has traveled to Ferguson, Detroit and black neighborhoods in major cities to talk about criminal justice reform.

Paul argued that Republicans have led on issues of criminal justice reform, and noted he was a co-sponsor of a bill passed late last year to require police departments to report all fatal police shootings to the Justice Department.

African Americans “end up getting no attention from either side,” Paul said. “Republicans don’t think they can win the black vote. Democrats think they’ve got it all.”

Republican campaigns, however, have not directly engaged with the Black Lives Matter movement, activists said.

Clinton’s campaign appears to be closely following Black Lives Matter, activists said.

But some activists say that she, too, appeared slow to catch on to the rhetoric of the movement. Last month, she endured some Twitter backlash during a speech at a black church near Ferguson when she drew a connection between her mother’s difficult early life and the struggles of many people today.

“What kept you going?” Clinton said she asked her mother. “Her answer was very simple: Kindness along the way from someone who believed she mattered.” Then Clinton added: “All lives matter.”

Some attendees said the remark made sense in context, but others were offended. One attendee told NPR that the comment “blew a lot of support” that Clinton had been building.

Though Clinton did not attend Netroots Nation, where she, too, might have faced demonstrators, she has joined her rivals in recent days in seeking to show solidarity with black activists and their cause.

“Black lives matter,” Clinton said in response to a question posed to her on Facebook by a Post reporter. “We need to acknowledge some hard truths about race and justice in this country, and one of those hard truths is that that racial inequality is not merely a symptom of economic inequality. Black people across America still experience racism every day.”

The post drew some praise from activists online. Mckesson, the organizer who had been invited to attend Clinton’s announcement speech, told his Twitter followers that the post was “solid.”

But he added a dose of skepticism: Compared to her rivals, after all, she got off easy.

“She also had time to craft it,” Mckesson wrote. “She should’ve been at Netroots.”