FBI Director James Comey has suggested police officers have been made gun shy by the prospect of getting caught on the next video of alleged police brutality. (Andrew Harnik/AP)

Twice in recent days, FBI Director James B. Comey has stepped to a podium here and asserted that police across the nation are reluctant to aggressively enforce the law in the post-Ferguson era of smartphones and YouTube.

And twice his comments have drawn disagreement and derision from a host of sources, including civil rights activists, law enforcement officials and, on Monday, the White House.

“The available evidence at this point does not support the notion that law enforcement officers around the country are shying away from fulfilling their responsibilities,” White House press secretary Josh Earnest said Monday at a news briefing in Washington. “The evidence that we’ve seen so far doesn’t support the contention that law enforcement officials are somehow shirking their responsibility.”

Comey, nonetheless, stayed the course, telling thousands of police officials gathered here for a conference of the International Association of Chiefs of Police that a violent crime wave is gripping the nation’s major cities. And he suggested that police officers themselves are in part to blame, made gun shy by the prospect of getting caught on the next video of alleged police brutality.

The “age of viral videos” has fundamentally altered U.S. policing, Comey said Monday in a speech virtually identical to one he delivered last week at the University of Chicago Law School.

His comments have been interpreted as giving credence to the notion of a “Ferguson effect” — the theory that riots and racial unrest in places such as Ferguson, Mo., and Baltimore, where police killed civilians, has prompted police officers to become more restrained. That, in turn, has theoretically resulted in an uptick in violent crime as criminals become emboldened.

Comey acknowledged Monday that he has little evidence to support the theory.

“The question is, are these kinds of things changing police behavior around the country? The honest answer is: I don’t know for sure whether that’s the case,” he said, but he added that “I do have a strong sense” it’s true.

It’s “the one theory that to my mind and to my common sense does explain” rising rates of urban violence in 2015.

Coming from the nation’s top law enforcement official, the remarks have landed like a bombshell in criminal-justice circles, offending people across the political spectrum. Civil rights groups and activists have taken deep exception to the idea that crime rates might be linked to protests against police brutality.

Amnesty International USA Executive Director Steven Hawkins called Comey’s comments “outrageous” and “unsubstantiated.”

Policing groups, meanwhile, have been equally infuriated by the assertion that their officers have been somehow derelict in their duties, frightened by teenagers with cellphone cameras.

“Time and time again [Comey] generalizes about a segment of the population that he knows nothing about,” said James O. Pasco Jr., executive director of the National Fraternal Order of Police. “He has never been a police officer.”

Comey is “like the scarecrow in ‘The Wizard of Oz,’ ” Pasco said. “He wanders around pretending to be smart and then at the end they give him a diploma and he thinks he’s a genius. They swear him in as the director of the FBI and all of a sudden he’s an expert on what police officers are thinking.”

The speeches also have put Comey at odds with the White House, as President Obama is eager to take credit for lowering the crime rate.

As Comey was preparing to deliver his address Friday, Obama was hosting a criminal-justice forum at the White House, where he celebrated “incredible, historic reductions in crime over the last 20 years.”

“I know that there’s been some talk in the press about spikes that are happening this year relative to last year. I’ve asked my team to look very carefully at it — Attorney General [Loretta E.] Lynch has pulled together a task force — and it does look like there are a handful of cities where we’re seeing higher-than-normal spikes,” Obama said at the time. However, he added, “across the 93 or 95 top cities, it’s very hard to distinguish anything statistically meaningful.”

In his speech Monday, Comey also urged law enforcement leaders to stop engaging in an us-vs.- them tug of war with protesters from Black Lives Matter, the group that sprung up in the wake of the August 2014 shooting of a black teenager by a white police officer in Ferguson.

Instead, Comey said, police chiefs should use the budding protest movement as a window into the minds of those they are charged with protecting.

“There is a line of law enforcement and a line of communities we serve, especially communities of color,” Comey said. “Each time somebody interprets ‘hashtag Black Lives Matter’ as anti-law-enforcement, one line moves away. And each time someone interprets ‘hashtag Police Lives Matter’ as anti-black, the other line moves away.”

Comey’s comments come weeks after he held a session with 100 city leaders and law enforcement officials from across the nation. At that meeting, many — including Chicago Mayor Rahm Emanuel (D) — reported that police morale was sinking in their towns amid ongoing scrutiny.

“We have allowed our police department to get fetal, and it is having a direct consequence,” Emanuel said during the meeting. “They have pulled back from the ability to interdict. . . . They don’t want to be a news story themselves. They don’t want their career ended early. And it’s having an impact.”

Comey said such feedback has served as inspiration for his recent speeches, in which he declared that violent-crime rates are being inflated by “a chill wind blowing through American law enforcement over the last year.”

“That wind is surely changing behavior,” Comey said, later adding: “We need to figure out what’s happening and deal with it now. I refuse to wait. . . . These aren’t data points — these are lives.”

In his speech, Comey also contradicted what has been the administration’s stance on the incarceration of thousands of men and women in the 1980s and 1990s related to the national drug war.

“Each drug dealer, each mugger, each killer and each felon with a gun had his own lawyer, his own case, his own time before judge and jury, his own sentencing, and, in many cases, an appeal or other post-sentencing review,” Comey said. “There were thousands and thousands of those individual cases, but to speak of ‘mass incarceration,’ I believe, is confusing, and it distorts an important reality.”

The Obama administration has worked to undo many of the policies that are credited with spurring a period of “mass incarceration,” and has boasted that 2014 was the first year in modern history that both the crime rate and number of federal prisoners declined.

“I can’t speak to the range of Director Comey’s views on this topic,” Earnest said when asked about Comey’s remarks on mass incarceration. “The president certainly does believe that there are certain elements of the criminal-justice system that are not serving the country in communities all across the country very well.”