What happens if federal agents and local officers stop getting along?

Normally, federal, state and local law enforcement officers are on the same side, investigating crimes, sharing leads and tracking down suspects.

But under the Trump administration, tensions between some local and federal officials have intensified over immigration sweeps, sanctuary city policies and the deploying of the National Guard to Democrat-run cities.

Those fissures widened this past week after an Immigration and Customs Enforcement agent shot and killed a woman in Minneapolis. State investigators said federal authorities excluded them from the investigation. After a shooting in Portland, Oregon, the next day that wounded two people, local police said they had received no information from federal officials, several hours after the episode.

Now politicians are publicly blasting one another, sparking even more corrosive disputes that will not make the arduous task of fighting crime any easier.

Minneapolis Mayor Jacob Frey told ICE to leave the city, saying in an invective-laden speech that the agency was harming public safety. In Philadelphia, District Attorney Larry Krasner warned ICE agents who intended to commit crimes to “get the eff out of here” or be prosecuted. California Gov. Gavin Newsom decried “masked men snatching people in broad daylight” and military operations in U.S. cities as “an assault on our values.”

Homeland Security Secretary Kristi Noem suggested that Minnesota authorities should focus on preventing violence and fighting fraud, a reference to allegations that hundreds of millions of dollars in federal aid had been misspent in the state. She denied that state investigators had been cut out of the shooting inquiry, saying instead they lacked jurisdiction.

Cooperation between federal authorities and state and local law enforcement is essential to holding drug gangs, other violent criminals and white-collar offenders accountable, law enforcement officials say. It is also routine, with countless task forces bringing together officers from multiple agencies to combat terrorism, sex and gun trafficking and white collar crime, as well as to track down suspects such as the one in a recent shooting at Brown University.

“I don’t know that we, at least in the United States, have lived this history before,” said Craig Futterman, who directs the Civil Rights and Police Accountability Project at University of Chicago Law School. He added, “This isn’t normal.”

State authorities can and do arrest and prosecute federal agents who violate the law, Futterman said, although agents who believe they were acting in the line of duty can request immunity in federal court. Investigations into such shootings are sometimes conducted by federal and local agencies in tandem.

More broadly, federal agents have traditionally notified local authorities of most planned operations, both as a matter of courtesy and safety. Agencies often collaborate, splitting up duties according to their strengths — for example, local police are generally more adept at crowd control during protests.

When such teamwork breaks down, said John Sandweg, who served as acting director for ICE during the Obama administration, “My answer is, we all lose.”

Sandweg acknowledged that ICE’s immigration enforcement has long been controversial in some areas, but said its investigations into crimes such as money laundering have relied heavily, and usually harmoniously, on cooperation with other agencies.

Turf wars among agencies are not exactly unheard of. But disagreements seem to erupt more sharply, more publicly and with less deference.

Even before the events of the past week, the district attorney in Uvalde, Texas, filed suit in May seeking to compel testimony from three Border Patrol agents who responded to the massacre at Robb Elementary School in criminal trials against a former local officer and police chief. Two of the agents participated in killing the gunman.

U.S. Customs and Border Protection responded in court filings that the information sought was already included in an agency report on the shooting, or that the information sought did not meet the legal standard of what would be considered necessary for the agency to provide.

On Friday, police in Anne Arundel County, Maryland, issued a statement publicly contradicting federal officials’ accounts of an earlier ICE shooting at a fleeing vehicle in the town of Glen Burnie.

And on Thursday night, Oregon Attorney General Dan Rayfield said his office would investigate the shooting by ICE agents in Portland. “We have been clear about our concerns with excessive use of force by federal agents in Portland and nationally,” he said in a statement.

Police leaders expressed fears that ICE tactics cast a shadow on the professionalism of their officers and would undo their efforts to gain public trust.

Sheriff Rochelle Bilal of Philadelphia called immigration agents “made up, fake wannabe law enforcement because what they do is against not only legal law but the moral law.” She added, “We have been fighting for years to build that trust between us and our communities.”

And though police unions are usually staunch advocates of officers’ right to defend themselves, one former union official, Charley Wilkison, former executive director of the Combined Law Enforcement Associations of Texas, the state’s largest police union, criticized what he called “newly recruited, masked” immigration agents.

In a Facebook post, he wrote that they would “no doubt damage and destroy the reputations of our proud and professional officers.”

For now, the Minnesota Bureau of Criminal Apprehension, which usually investigates police shootings, remains sidelined in the matter of Renee Nicole Good, the woman killed in Minneapolis. But, the bureau said in a statement, “The BCA remains open to conducting a full investigation of the incident should the U.S. attorney’s office and FBI reconsider their approach.”