(CNN) The forced separation of children from their parents upon trying to enter the US illegally has become, over the course of the past 96 hours, a massive national issue. A handful of congressional Democrats -- including Sens. Jeff Merkley (Oregon) and Chris Van Hollen (Maryland) -- visited a detention center in McAllen, Texas, on Sunday, drawing even more attention to the issue. And President Donald Trump launched a tweetstorm Monday morning regarding forced separation; "It is the Democrats fault for being weak and ineffective with Boarder Security and Crime," he tweeted . "Tell them to start thinking about the people devastated by Crime coming from illegal immigration. Change the laws!"

The issue has risen so rapidly -- and so quickly become a political football -- that many people, me included, have struggled to decipher who's telling the truth, who's not and how to solve this problem. For answers, I reached out to Doris Meissner , the director of the US immigration policy program at the Migration Policy Institute. Meissner is also a former commissioner at the Immigration and Naturalization Service, where she served from 1993-2000.

Our conversation, conducted via email and lightly edited for flow, is below.

Cillizza: Prior to Donald Trump taking over as President, what was the policy toward undocumented immigrants entering the country with small children?

: Before the Trump administration's zero-tolerance policy , families arriving at the border without authorization to enter but claiming a credible fear if returned home were permitted to enter to apply for asylum. Whether or not they were detained while applying for asylum depended on a series of court rulings and legislation, in addition to the availability of detention bed space.

A 1997 court settlement agreed to by the US government in a case called Flores v. Reno , which remains in effect today, requires the government to release children from immigration detention without unnecessary delay to, in order of preference, parents, other adult relatives or licensed programs willing to accept custody. If children cannot be released, Flores requires the government to hold them in the "least restrictive" setting available. The 2008 Trafficking Victims Protection Reauthorization Act , signed by President George W. Bush, codified parts of the settlement into federal law.

In 2015, a federal judge in California ruled that the Flores requirements apply not only to unaccompanied minors but also to children apprehended with their parents, meaning that all minors must be released from detention if possible. The judge also ordered the Department of Homeland Security to release parents detained along with their children. An appeals court in 2016 affirmed that Flores applied to all children but reversed the ruling that parents should be released as well.

Amid a surge in family flows, there were not enough detention beds available to hold families even for the 20 days allowed under the court settlement, causing many to be released. The family detention system currently has capacity to hold just 2,700 people at a time -- resulting in the "catch and release" that President Trump railed against in his election campaign and since.

Cillizza: What, specifically, did the Trump administration change in this policy? And is this simply an enforcement of an Obama administration policy or an actual change?

Meissner: The change the Trump administration has made is to declare and try to implement a zero-tolerance policy at the US-Mexico border: Criminal prosecution of all people who seek to cross illegally between ports of entry. With Attorney General Jeff Sessions' announcement on April 7 that all illegal crossers would be prosecuted in federal court for illegal entry or re-entry, the administration essentially ensured that parents would be separated from their children because minors cannot be kept in federal criminal detention facilities. So the parents are now being transferred from the Border Patrol to the US Marshals Service and then are being tried in court for the misdemeanor of illegal entry or the felony charge of illegal re-entry. As a result, their children are turned over to the custody of the Department of Health Human Services' Office of Refugee Resettlement.

The Trump administration's blanket policy to prosecute all illegal crossers, including family groups, is new. However, it builds upon earlier efforts by the Bush and Obama administrations. In 2005, the Bush administration launched Operation Streamline in one Border Patrol sector in Texas, aiming to criminally prosecute illegal crossers. Between 2003 and 2005, criminal prosecutions of first-time unauthorized crossers for illegal entry or re-entry more than quadrupled, from 4,000 to 16,500. By 2010, they had reached 44,000. Operation Streamline was extended to some other Border Patrol sectors and continued under the Obama administration, reaching a peak 97,000 criminal prosecutions in 2013.

Still, the phenomenon of families arriving at the US-Mexico border together dates from just the last few years, and was not one that the Bush or early Obama administrations confronted in any significant numbers. Few children were separated from their families during the earlier administrations as a result of criminal prosecution of the parents.

Cillizza: Was this outcome -- lots of young children being separated from their parents -- expected? Is it worse than people thought?

Meissner: We don't know what the internal deliberations and planning were within the administration. But it seems obvious that there should have been immediate recognition that implementation of a zero-tolerance policy would almost instantly result in a de facto policy of family separation. Accordingly, the federal Office of Refugee Resettlement, which was already dealing with significant capacity issues surrounding the care of a separate flow of unaccompanied minors, would need to be in position to provide additional housing and care for a child population that is uniquely vulnerable.

ORR's job in dealing with unaccompanied minors is to seek to reunite children with relatives already in the United States. The difference now is the agency, which is an arm of the government that has deliberately separated these families, is dealing with children who are traumatized by that separation as well as any traumas they suffered along the migration journey or in their country of origin. With reports that ORR is opening a tent city for children in El Paso, has contracted with a service provider to house children in a former Walmart, etc., the capacity issues are proving significant -- and are likely to continue as long as the zero-tolerance policy continues.

Cillizza: Where do we go from here? Trump keeps calling for a bipartisan solution from Congress. Is that an option? And what would it look like?

Meissner: This is a remarkably complex situation and there is no good policy solution.

Arrivals of Central American families at the US-Mexico border have been increasing. Fewer than 1,000 people traveling together in families were apprehended in May 2012. In May 2014, nearly 12,800 were apprehended. Although the number was a lower 9,500 in May 2018, these so-called "family unit" arrivals have overtaken unaccompanied minor apprehensions, raising concerns within DHS and the Trump administration more broadly. At the same time, a policy that results in the deliberate separation of children -- sometimes very young ones -- from their parents is not humane, and there are even questions whether it will prove effective over the long term in deterring future arrivals.

At a broad level, a number of things should happen. Most important would be to recognize that within these family flows are many who have grounds to assert a humanitarian protection claim. The administrative immigration courts system is struggling with huge backlogs, and the two and three years for the average case to get to a hearing represent in many ways a pull factor for people to come, knowing a decision on their future could be far off.

Congress should continue to fund resource increases so the courts can fairly, fully, transparently and efficiently adjudicate asylum claims as part of the removal process for deciding immigration cases. Doing so, of course, is not an overnight solution. So as an immediate step, the administration has other options, including not separating families and instead using ankle-monitoring bracelets or other alternatives to detention to ensure people show up for their court hearings. Alternatives to detention have been effective and are far less costly than detention -- certainly in human terms, weighing the current family separation traumas but also financially.

There are many other deeper policy needs to address -- including finding ways to strengthen institutions and economies in Central America to reduce the push factors driving this migration and assisting with reintegration so that returnees aren't forced to set out again.

Cillizza: Finish this sentence: "The result on immigration policy of images of young children being taken from their parents will be ______________." Now, explain.

Meissner: "One that should serve as common ground to unite Republicans and Democrats for the first time in a long time in agreeing on a solution."

Amid what seems to be near-universal condemnation of family separation, including by traditional allies of this administration, Congress could come together in a bipartisan fashion to address this. Unfortunately, as is almost always the case when dealing with immigration policy and politics, significant potential exists for this pressing family-separation issue to become ensnarled in other important and long-unresolved immigration policy topics. Still, seeing the public outcry and consternation from elected officials from both political parties, one has to wonder how much longer the administration can sustain this policy.