Former President Barack Obama made an impassioned plea in a Facebook post Wednesday for the end to a federal policy that separates migrant families at the U.S. border, appealing to Americans' moral consciousness — and without mentioning political affiliations — to get his point across.

"To watch those families broken apart in real time puts to us a very simple question: Are we a nation that accepts the cruelty of ripping children from their parents' arms, or are we a nation that values families, and works to keep them together?" Obama wrote on the occasion of World Refugee Day.

"Our ability to imagine ourselves in the shoes of others, to say, 'There but for the grace of God go I,' is part of what makes us human," he said, adding that Americans should "prove" who they are "through our policies, our laws, our actions and our votes."

His comments came an hour or so before President Donald Trump signed an executive order that would allow children to be held in detention alongside their parents, backing down from the administration's policy to separate them.

So far this spring, more than 2,300 migrant children have been separated from their parents, many processed at a facility in the border city of McAllen, Texas. Attorney General Jeff Sessions announced last month that the government would criminally prosecute anyone who crosses the U.S.-Mexico border illegally.

Here are the latest developments:

Trump signed an executive order to keep children with their parents when families are detained at the border. Read more about the order here.

Amid reports this week of children inside encampments of metal fencing and left wailing inconsolably, Trump on Twitter continued to blame Democrats for the escalating crisis as some prominent congressional Republicans — facing political backlash — lined up against the "zero tolerance" policy.

At the McAllen processing station, security contractors are posted at watchtowers. Those towers observe all groups of detained migrants, including those in a recreation area specifically set aside for mostly "tender age" children who are without families. NBC News toured the enclosure on Sunday, but was not aware of the recreation area. Read more about the McAllen center here.

In some cases, "tent cities" in Texas have been constructed to house the migrants. The cost of holding migrant children is $775 per person per night, according to a Department of Health and Human Services official — far higher than the cost ofkeeping children with their parents in detention centers or holding them in more permanent buildings. Read more about the costs here.

American Airlines said it was asking the federal government to refrain from using its flights to take children away from their families. In addition, United Airlines and Frontier Airlines said they don't want to be used that way — prompting a Department of Homeland Security spokesman to criticize the "unfortunate" decision in a series of tweets.

Pope Francis and British Prime Minister Theresa May are among the international leaders to condemn the Trump administration's policy. Read more about their criticism here.

Many of the families being held at the border are fleeing deadly violence in Central America. Child migrants traveling alone must be sent to facilities run by HHS within three days of being detained. The agency is then responsible for placing the children in shelters or foster homes until they are united with a relative or sponsor in the community as they await immigration court hearings.

A "tent city" recently built near the Tornillo Port of Entry in Tornillo, Texas. Joe Raedle / Getty Images

The government's effort to prosecute all border crossers has led to the breakup of migrant families and sent a new group of hundreds of young children into the government's care.

Congress had been unable to agree on an immigration bill that could end the separation policy as well as offer certain undocumented immigrants a pathway to citizenship. Trump has remained more hard-line on changes, and has sought a crackdown on asylum seekers and the building of a wall along the Mexico border.

Homeland Security Secretary Kirstjen Nielsen falsely claimed on Monday that the Obama administration "separated families ... their rate was less than ours, but they absolutely did do this."

Immigration advocates and former Obama administration officials shot back that there was no widespread practice of separating children from their parents.

Students and alumni at Berkeley Preparatory School, a private Episcopal institution in Tampa, Florida, from which Nielsen graduated in 1990, urged the school to condemn the policy.

"We do not have faith in Secretary Nielsen to live the values of our alma mater or to make any decisions concerning outcomes for children at the border," they said in a letter to administrators, which was signed by more than 600 students and alumni.

"It wasn't until the press conference with Kirstjen that we realized she had just become the undeniable face of this policy, and we had to mobilize immediately," said one of the organizers, Megan Magray, a 2013 graduate who is a nonprofit communications specialist in Brooklyn, New York.

The school said in a statement that its role "is not and cannot be to take a position on non-education-related governmental policy or action."

An accompanying fundraising campaign for the Refugee and Immigrant Center for Education and Legal Services, an advocacy group in Texas, had taken in a little more than $10,000 of its goal of $25,640, which organizers said is Berkeley's average annual tuition.