NEW YORK — It felt like a watershed moment for a scattered and still-young civil rights movement.

Inside Black Lives Matter, the national revulsion over videos of police officers shooting to death black men in Minnesota and Louisiana was undeniable proof that the group’s message of outrage and demands for justice had finally broken through.

Even the white governor of Minnesota, Mark Dayton, in a pained public concession, embraced the movement’s central argument. “Would this have happened if those passengers — the driver and the passengers — were white?’’ he asked. “I don’t think it would’ve.’’

Then, in an instant, everything changed.

Black Lives Matter now faces perhaps the biggest crisis in its short history: It is both scrambling to distance itself from a black sniper in Dallas who set out to murder white police officers and trying to rebut a chorus of detractors who blame the movement for inspiring his deadly attack.

“What I saw in Dallas was devastating to our work,’’ said Jedidiah Brown, a Chicago pastor who has emerged as an outspoken Black Lives Matter activist over the past year. The moment he learned of the attack on the police, he said, he immediately sensed that any emerging national consensus would “tear down the middle.’’

“The thing I vividly remember thinking was, this is going to show exactly how divided this conversation is,’’ he said.

For those who have harbored doubts or animosity toward Black Lives Matter — among them police unions and conservative leaders — the Dallas attacks are a cudgel that, fairly or not, they are eager to swing.

In Texas, several state officials, including Lieutenant Governor Dan Patrick, lashed out at the group, directly linking its tone and tactics to the killings. Patrick acknowledged that the demonstration in Dallas on Thursday night had been peaceful until the gunman struck, but he accused the movement of creating the conditions for what happened.

“I do blame former Black Lives Matter protests,’’ he said.

“This has to stop,’’ Patrick said, adding of the police officers, “These are real people.’’

State Representative Bill Zedler, a Republican, was equally blunt in his assessment of the group’s influence on the 25-year-old gunman, Micah Johnson.

“Clearly the rhetoric of Black Lives Matters encouraged the sniper that shot Dallas police officers,’’ he wrote on Twitter.

But a bigger problem for Black Lives Matter, supported by many liberals, is that Johnson’s actions could jeopardize the movement’s appeal to a broader group of Americans who have gradually become more sympathetic to its cause after years of highly publicized police shootings.

In the days before the Dallas massacre, Aesha Rasheed, 39, an activist in New Orleans, felt that at long last, white and black America were watching the same images with the same horror: two Louisiana police officers tackling and then shooting Alton Sterling, 37; the body of Philando Castile, 32, after a Minnesota police officer shot him through a car window, with his girlfriend and her daughter sitting inches away.

“It seemed like a national consciousness was sinking in,’’ Rasheed said. After the massacre in Dallas, she said, “it turned on a dime.’’

She now worries that the episodes involving black men may be overshadowed and overlooked. “Does this get ignored?’’ she asked. “Do five officers take center stage?’’

Black Lives Matter usually spurns central planning and management. But in a sign of alarm over the volatile situation, leaders of several organizations associated with the movement put out formal statements that repeatedly described the Dallas attacker as a lone gunman, unconnected to the group’s cause.

“There are some who would use these events to stifle a movement for change and quicken the demise of a vibrant discourse on the human rights of Black Americans,’’ read a statement from the Black Lives Matter Network. “We should reject all of this.’’

Police have said Johnson had no direct links to any protest group. But in recounting Johnson’s final hours, Chief David O. Brown of the Dallas Police Department mentioned the movement by name. “The suspect said he was upset about Black Lives Matter,’’ he said.

Black Lives Matter was born as a rallying cry, after the 2013 acquittal of George Zimmerman in the Florida shooting death of Trayvon Martin, an unarmed African-American 17-year-old.

By the time demonstrators took to the streets of Ferguson, Mo., a year later to protest the killing of Michael Brown, another unarmed African-American, it was the motto and name of a decentralized collection of activists.

Last week, activists scoffed at calls to recalibrate their message or their strategy.

By Friday night, protesters had returned to the streets in multiple cities. But it was clear that the national conversation had changed.

On social media, Black Lives Matter activists watched with dismay on Thursday night as a squall of outrage and mourning over the shootings of Sterling and Castile was suddenly overwhelmed by a furious outcry over the shooting of Dallas police officers and messages of rage directed at activists and protesters.

Sitting in his bed after midnight with an iPhone, DeRay Mckesson, 30, a Black Lives Matter activist, watched the rapid change in tone. “It suddenly became about blame,’’ he said. “People wanted to link it to the protesters no matter what.’’