Hundreds of immigrant children have been separated from their parents at the border since October, and the Justice Department’s new policy calling for criminal prosecutions of all those who cross illegally promises to increase that number drastically.

President Donald Trump and his aides at the White House have pushed a family separation policy in order to deter Central American families from trying to cross the border illegally, according to administration officials. The number of families making the journey over land to the United States has soared in recent months after subsiding last year, infuriating the president, who had touted the initial decline as proof that his tough stance on immigration was ­succeeding.

Here’s a look at what is happening to migrant families on the border, and what’s behind it.

Is there a new policy to separate parents from their children at the border?

The administration did not announce a blanket policy to separate families.

Attorney General Jeff Sessions said his department would criminally prosecute everyone who illegally enters the United States. If a mother or father is with a child when apprehended for the crime of illegal entry, the minor must be taken from the parent. The child cannot remain with a parent in the criminal court system.

Is the administration deliberately breaking up families?

Administration officials say the aim is to protect the border and uphold the law through new measures to deter illegal immigration.

Other motivations: Sessions has said the asylum system is overwhelmed with people making frivolous claims, and Trump, according to administration officials, had been demanding that families be broken up to stanch the flow of Central Americans to the border. The majority of apprehended migrants hail from Honduras and El Salvador, two countries wracked by violence. Children are often targeted for recruitment by gangs, and their families seek a haven in the United States.

Nearly 80,000 people came as members of family units between October, the beginning of the current fiscal year, and April. About 14,000 came in March; about 15,000 in April.

When did the separations begin?

Immigration lawyers and advocates who work at the border say family separations began after Trump took office pledging to crack down on illegal immigration, though a very small number occurred during previous administrations.

The practice gained momentum in the past two months, particularly in Texas, where many families from Central America seek to cross, they say.

“What we saw in El Paso was a massive increase in cases of families being separated at the border,” said Laura St. John, legal director of the Florence Project, a nonprofit that offers legal education to migrants in detention facilities.

In California, public defenders said they had not seen the practice until a recent caravan of Central Americans traveling through Mexico to the U.S. border grabbed headlines and drew Trump’s ire.

“We began to hear rumors that separations were happening a couple months ago, but hadn’t encountered any,” said Reuben Cahn, executive director of the Federal Defenders of San Diego, who is representing several of the caravan migrants.

Is anyone challenging the policy?

The American Civil Liberties Union is seeking a nationwide injunction against the practice. The organization argues in its lawsuit that it is a violation of due process to separate parents and children simply as a means to deter illegal immigration. Only parents who are abusive or unfit to care for their children can legally have them taken away, the suit argues.

In the lawsuit, filed before the administration announced the new practice, the ACLU accused the Homeland Security Department of unlawfully separating a Congolese woman and her 7-year-old daughter who had sought asylum.

Are there other reasons that families are being separated?

Logistics are a factor. The nation’s two family detention centers, where families can remain together while awaiting disposition of their cases, have a combined capacity of just 2,700 people.

The other option is to release parents and their children with orders to return to court for their immigration hearings. That has often been the practice until now.

What is happening to the children?

The government says that once it decides to detain a parent, it cannot release a minor without providing a guardian for that child. As a result, it sends children to federal detention facilities while the parent remains in the criminal justice system.

A child can be released to another guardian, say, a family member, if one is available and can prove ties.