Attorney General Jeff Sessions, in his first significant speech as the nation’s top law enforcement official, warned that recent increases in serious crime might portend a violent new period in the country’s history and vowed to work to stop it.

Speaking to the National Association of Attorneys General on Tuesday, Sessions said that the country has seen warning signs, and that he fears that the era of historically low crime rates might be coming to an end. He said law enforcement can’t become “overconfident” because violence is near historic lows, and he cited rising crimes rates in the 1970s as an indicator of what might happen.

“We’ve done a lot of good. We need to not give up on that progress,” Sessions said. “That is the thing that has concerned me the most.”

Sessions, a Republican former senator from Alabama, has long spoken of reinvigorating the fight against violent crime, and his bleak view of the United States is in line with that of President Trump, who has cast his administration as one that values law and order. Sessions’s remarks confirm that he is likely to break with his predecessors in President Barack Obama’s Justice Department, who worked to grant clemency to drug and other offenders they said were serving sentences far out of proportion with the crimes they committed.

Attorney General Jeff Sessions is greeted by employees as he arrives at the Justice Department in Washington. (Susan Walsh/Associated Press)

Sessions has deviated from past administrations in other areas. He said in a recent memo that the Justice Department will continue to use private prisons, contrary to a directive from Sally Yates when she was deputyattorney general. He similarly revoked guidance from the prior administration on students being allowed to use the bathrooms matching their gender identities. And on Monday, his Justice Department dropped its long-standing position that Texas intended to discriminate when it passed a strict voter-ID law.

On crime and drugs, Sessions seems likely to take a harder stance than those of his predecessors. He spoke to reporters Monday and to the attorneys general Tuesday about how he does not think marijuana should be legalized, and he said that he will revisit guidance from former deputy attorney general James Cole on how federal authorities should act in states that have done so.

Cole had written that in states with robust regulatory systems, federal officials should continue to leave the matter to local law enforcement. But states without such systems might face challenges from the federal government, Cole wrote.

“States, you know, can pass whatever laws they choose, but I’m not sure we’re going to be a better, healthier nation if we have marijuana being sold at every corner grocery store,” Sessions said Tuesday. “We’ll have to work our way through that.”

Sessions said that increases in crime tend to follow increases in drug use, and he worried about “the beginning of a trend.”

Combating violent crime has been a signature issue for both him and Trump. Less than a month into office, Trump signed three executive actions directing the Justice Department to form a task force and take other steps to target criminal gangs, and reduce violent crime and attacks on police.

In his speech, Sessions — unlike Trump — offered context for his warning about rising crime. He cited data showing that homicides had increased by nearly 11 percent from 2014, and said he did “not believe that this pop in crime, this increase in crime is necessarily an aberration, a one time blip.” But he also noted the homicide rate had been cut in half from what it once was.

Sessions also seemed to foreshadow a Justice Department that is friendlier to police than it had been in the past, and perhaps less likely to prosecute officers when they are accused of wrongdoing. He said he had not decided how to proceed with a possible consent decree mandating reform at the Chicago Police Department — where a Justice Department investigation found officers routinely use excessive force — and even suggested that less heavy-handed policing may be to blame for that city’s increase in crime

“One of the metrics that has been reported in Chicago shows a dramatic reduction in stops and arrests in Chicago by the police department,” he said. “That has got to be a factor in the increase in violence in the city.”

Sessions said he had not read reports on the police departments in Chicago and Ferguson, Mo., where 18-year-old Michael Brown was fatally shot by a police officer, sparking riots, but he minimized the summaries he had reviewed. “Some of it was pretty anecdotal and not so scientifically based,” he said.

In his speech, he also suggested that second-guessing of police is hindering the fight against crime.

“Somehow, some way, we’ve undermined the respect for our police, and made, oftentimes, their job more difficult, and it’s not been well received by them, and we’re not seeing the kind of effective community-based, street-based policing that we found to be so effective in reducing crime,” he said.