If there's one issue animating the presidential campaign of frontrunner Donald Trump, it's America's 11.3 million illegal immigrants, many of whom Trump says he would deport. Along with the practical difficulties of doing so, however, new research shows the devastating effects on children when their parents are sent back home.

The Obama administration has already expelled about 3.7 million people who were living here illegally between 2009 and 2013. While the pace of deportations has slowed dramatically, with a shift in enforcement towards weeding out those who have actually committed crimes in America, the Migration Policy Institute estimates that several hundred thousand children have either one or no parents in America as a result. And 5.3 million children are still living with unauthorized parents, constantly under threat of losing one or both.

We're just starting to understand the impact that losing a mother -- or, much more often, a father -- can have on those kids' development.

A pair of reports issued Monday paint a broad picture of how kids have been affected by deportations in the past several years. Both were funded by the U.S. Department of Health and Human Services and conducted by the Migration Policy Institute and the Urban Institute, with help from research and input from U.S. Immigration and Customs Enforcement.

The first, a survey of smaller-scale studies conducted on unauthorized immigrant families, shows that the effects of losing a parent to deportation are basically the same as what happens when a parent goes to prison: Kids can become homeless, bounce around to different family members, lose focus in school, and undergo long-lasting psychological trauma. One study found that family income dropped by 70 percent in the six months following a deportation, and one quarter of families in that situation reported going hungry.

The second, a synthesis of field work at study sites in California, Florida, Texas, South Carolina, and Illinois, found all of those impacts -- and also identified gaps in social services that are ill-equipped to handle the special needs of children whose families have been ruptured by immigration rules.

“Study participants reported that children refused to eat, pulled out their hair, or had persistent stomachaches or headaches," the authors write. "Others turned to more self-destructive outlets such as cutting themselves or abusing substances."

Academic performance also generally suffers in the wake of a parent's deportation, as one grandmother in the Rio Grande Valley reported happening to her grandson. “He was hardworking, he was doing well in school," she told researchers. "But after all that, he would not go to school, he wouldn’t work, he just sleeps during the day and is out at night. He’s on a bad path now, he’s always going to court.”

Depression doesn't only hit kids whose parents have disappeared, the Migration Policy Institute's research found. It also impacts their spouses, most of whom were not the family's primary breadwinner, and have trouble replacing the income they lost. Immigrant parents already tend to be reluctant to apply for social welfare benefits, even if their children -- many of whom are U.S. citizens -- are eligible. Along with the inability to apply for drivers licenses and poor public transportation, that reduces access to healthcare and other services for their kids.

As Pamela Constable reports for The Post today, having a child is already difficult enough for immigrant mothers, and is only made worse when fathers are suddenly subtracted from the equation. Child welfare agencies often lack the expertise to deal with custody issues related to deportation proceedings, nevermind basic Spanish skills.

The Obama administration's proposed Deferred Action for Parents of Americans program would have allowed parents to request temporary legal residence and work authorization if they pass a background check and have resided in the United States since 2010, freeing families from fear of separation. The executive order was blocked by a judge this past February and has not gone into effect.