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President Trump has made crime a key issue in his reelection campaign. His Justice Department has sent federal agents to tamp down riots and to crack down on gun violence in swing states. But criminologists worry the Trump administration's actions are simply to gain political advantage in November. NPR national justice correspondent Carrie Johnson reports.

CARRIE JOHNSON, BYLINE: The Democratic mayor of Kenosha, Wis., had asked President Trump not to visit this week because his city is still recovering from violence that burned down buildings and shuttered small businesses. The president traveled there anyway.

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PRESIDENT DONALD TRUMP: Kenosha has been ravaged by anti-police and anti-American riots.

JOHNSON: Demonstrations erupted after a white police officer fired seven shots into the back of a Black man named Jacob Blake. Then, a white teenage suspect who reportedly supports President Trump shot three protesters, killing two of them. Trump defended the teen, explaining he might have acted in self-defense. During the visit, Trump offered praise for Republican elected officials in Wisconsin, a battleground state. And he went out of his way to attack Democrats in other big cities nearby.

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TRUMP: Obviously, that's been a disaster, Chicago, total disaster, with, again, radical left Democrat. And we just have to - it's all Democrat. Everything's Democrat. All of these problems are Democrat cities. We don't want to say it, but it is.

TRUMP: At the president's side was Attorney General Bill Barr. His Justice Department says it's investigating whether the policeman who shot Jacob Blake broke civil rights laws. Barr promised the officer would get due process, and then added this.

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BILL BARR: Once again, we saw the hijacking of a protest by a hardcore group of radicals who were carrying out planning a coordinated violent attack on law enforcement, on public property and on private property. And that can't be tolerated.

JOHNSON: Barr has pointed to so-called radicals as a source of anarchy at protests across the country. Yet, that isn't borne out in the criminal charges that federal prosecutors have brought to date. The action by the Trump administration isn't happening in a vacuum. The president is making crime and social unrest a key message in his campaign. Trump's Democratic opponent, Joe Biden, cries foul.

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JOE BIDEN: Donald Trump looks at this violence and he sees a political lifeline.

JOHNSON: For its part, Trump's Justice Department says it's taking steps to maintain order. It sent federal agents to nine cities led by Democrats where violent crime has spiked this year. But it hasn't moved that program, called Operation Legend, into places like Tulsa, Okla., which is run by a Republican mayor.

The Justice Department also launched a second effort - a surge of agents to cities facing riots. Some mayors and governors have refused the officers, and critics said many of the agents had no training for dealing with protesters. Richard Rosenfeld is a criminologist at the University of Missouri, St. Louis.

RICHARD ROSENFELD: In particular, federal agents who are not trained in local policing, who have no knowledge of the local area - from of criminological point of view, it's just mind-blowing to think that a couple of hundred of folks who are not trained and unfamiliar with the area are going to help out very much.

JOHNSON: Rosenfeld says the rise in murders and aggravated assaults this year should trouble people. But he says there is not enough data to link those problems to protests over police violence. The pandemic has cost millions of jobs and made people worry about their next meal. Rosenfeld says it's also limited the way many of the best police do their jobs, getting out of their cars and talking to people face-to-face.

ROSENFELD: And we have to subdue the virus in order to increase police effectiveness and effectively confront this rise in violent crime.

JOHNSON: Experts say they know what it takes to reduce crime and restore trust in police. But it takes political will to get that done.

Carrie Johnson, NPR News, Washington. Transcript provided by NPR, Copyright NPR.