The militarization of America's police has been hotly debated in recent years. Critics argue that effectively turning cops into soldiers risks alienating them from the communities they supposedly serve.

New research provides evidence supporting such warnings. It finds the use of SWAT teams—perhaps the most common and visible form of militarized policing—neither reduces crime nor enhances public safety.

It reports this aggressive approach to law enforcement is disproportionately used in minority communities. And finally, it finds portraying officers in military gear decreases public support for the police.

"Curtailing militarized police may be in the interest of both police and citizens," concludes Jonathan Mummolo, an assistant professor of politics and public affairs at Princeton University. His study is published in the Proceedings of the National Academy of Sciences.

Mummolo measured the impact of militarization using a variety of methods. Among his data sources were "a nationwide panel measuring the presence of active SWAT teams," and a list of every SWAT team deployment in the state of Maryland over a five-year period (8,200 in all).

"SWAT teams," he notes, "often received advanced combat training," and their formation "represents a heightened commitment to the use of militarized equipment and tactics."

He found "the vast majority of SWAT deployments occur in connection with non-emergency scenarios, predominately to serve search warrants." What's more, these teams "are more often deployed in areas with high concentrations of African-Americans, even after adjusting for local crime rates."

Perhaps most importantly, he reports "there is no evidence that acquiring a SWAT team lowers crime, or promotes officer safety." All in all, he adds, "the benefits of increased deployments appear to be either small or nonexistent."

But there are costs involved, as the second part of the study shows. Mummolo conducted two studies of Americans' attitudes toward the police: one online, featuring 1,566 people, and another conducted by Survey Sampling International, featuring 4,465 people.

Participants read a fictitious news article in which a police chief argues his department deserves a larger budget. The report was paired with a one of four photos featuring a group of policemen "standing guard during a local protest."

The images depicted various degrees of militarization, ranging from one in which five officers stand in traditional uniforms to another featuring cops in riot gear posing with an armored vehicle. Participants were then asked about their support for police spending and their confidence in the force.

The results: Seeing the armored-vehicle photo "caused support for police funding in the United States to fall by roughly four points in the (online) survey, and two points in the SSI survey," Mummolo reports. "Support for funding the department in the news article also fell."

Strikingly, among people taking the latter survey, viewing that image also led to "a 3.2 point drop in respondents' desire for more police patrols in their own neighborhoods."

It seems few people are enthused about having a pseudo-army patrolling their streets. And they assume a police force that can afford that kind of equipment doesn't need additional taxpayer dollars.

Overall, "the routine use of militarized police tactics by local agencies threatens to increase the historic tensions between marginalized groups and the state, with no detectable public safety benefit," Mummolo concludes. "While SWAT teams arguably remain a necessary tool for violent emergency situations, restricting their use to those rare events may improve perceptions of police with little or no safety loss."

Attorney General Jeff Sessions might want to rethink his support for a plan in which surplus military gear is passed on to police forces. This research suggests the benefits are negligible at best, while the costs are quite real.