President Trump claims his administration’s new and expansive executive order on undocumented immigrants is "getting really bad dudes out of this country." But aggressive enforcement of immigration laws is also sweeping up vulnerable, far-from-bad people seeking help and care. Still, even setting aside the humanitarian issue, Trump's anti-immigrant plan suffers from a fundamental flaw: bad math.

The new immigration guidelines released by Department of Homeland Security chief General John Kelly this week broaden the categories of people prioritized for deportation. Instead of focusing on violent criminals, the department will now go after anyone who's ever committed fraud or misrepresented themselves to the US government—a description that essentially includes anyone who's ever lived in the country illegally. The department claims its expanded plan will enhance public safety. But adding millions of new potential "criminals" to the list goes against prevailing trends in policing toward tech-driven, targeted enforcement. In other words, by making everyone a criminal, the administration will have a tougher time cracking down on real crime.

"Most probabilistic approaches to predicting crime are about trying to narrow the set of potential points of interdiction, not expanding them," says Jeff Brantingham, a UCLA anthropologist who has worked on predictive policing tools.

Policing has come a long way from the dragnet days of the 1950s. Today, police departments are rapidly integrating data and machine learning algorithms to weed out low-level offenders from the system and divert those resources to catching and rehabilitating actually dangerous criminals. These tactics come with their own problems: some predictive technologies have exhibited serious racial biases. But even Democrats and Republicans have agreed in recent years that finely tuned policing is smart policing.

"This is dumb policing," says Richard Berk, a University of Pennsylvania criminologist and statistician, of Trump's deportation plan. Berk has developed machine learning tools that help the city of Philadelphia make probation decisions by analyzing an offender's likelihood to pose a future risk. So far, he says, it's helped the city save resources, and re-arrests haven't gone up.

Trump's plan, he says, takes precisely the opposite approach, vastly increasing the resources the government will need to root out undocumented immigrants without guaranteeing that the fraction of the population that actually poses a risk is being deported. "It means that you'll work just as hard to find undocumented individuals who are virtually guilty of nothing except being undocumented as finding individuals who are committing serious crimes," he says. "That just makes no sense."

Consider the numbers. During the campaign, Donald Trump Jr. tweeted a photo of a bowl of Skittles with the caption, "If I had a bowl of Skittles and I told you just three could kill you, would you take a handful?" (In case you missed Trump's analogy comparing humans to candy, the Skittles represent refugees.) Turns out the president's son's tweet isn't just cruel and insensitive; he also relies on faulty statistical reasoning. Given the rate of violent crimes committed by refugees, you'd have to hunt through a swimming pool of Skittles, not a bowl, to find those three poisonous treats. Now apply that to Trump's immigration plan. Adding all 11 million undocumented immigrants to Homeland Security's list means immigration enforcement officials now face a radically larger population to sift before they find truly dangerous people.

"If one starts with a pool of potential criminals that is identified for targeting, and then adds to this pool the set of undocumented immigrants who, on the whole, certainly have a lower crime rate, then the overall crime rate of the combined pool is smaller than the original one," says Mark Glickman, Harvard University statistician.

When it comes to public safety, however, Trump's approach has an even bigger problem. Do undocumented immigrants commit violent crimes? Yes. But they don't commit them at a greater rate than the rest of the US population. Singling out undocumented immigrants for enforcement is not a strategy for fighting violent crime. It's a strategy for fighting immigrants.

'Most probabilistic approaches to predicting crime are about trying to narrow the set.'

"All of these executive orders and everything we’ve seen coming down the pike all rest on the assumption, an erroneous assumption, that immigration and crime go hand in hand," says Charis Kubrin, a UC Irvine criminologist. "The literature shows nothing to prove that."

Kubrin and her colleague Graham Ousey of the College of William and Mary recently analyzed more than 50 studies related to immigration and crime published between 1994 and 2014. Their findings, which will be published in the The Annual Review of Criminology, show no correlation between immigration to an area and increases in crime. Where there was any relationship at all, Kubrin says, it was a negative one— in other words, more immigration corresponded to less crime.

For all his talk of booting "bad hombres" out of the US, Trump's executive order is more likely to result in the haphazard deportation of just about anyone, bad or not. Ordinary people are already being dragged away from their families and out of hospital beds. Under Trump's plan as currently designed, that's a feature, not a bug.