The “zero-tolerance” policy he announced [in May 2018] sees adults who try to cross the border, many planning to seek asylum, being placed in custody and facing criminal prosecution for illegal entry.

As a result, hundreds of minors are now being housed in detention centres, and kept away from their parents.

Over a recent six-week period, nearly 2,000 children were separated from their parents after illegally crossing the border, figures released on [15 June 2018].

[Attorney General] Sessions said those entering the US irregularly would be criminally prosecuted, a change to a long-standing policy of charging most of those crossing for the first time with a misdemeanour offence.

Until May 2019:

It has long been a misdemeanor federal offense to be caught illegally entering the US, punishable by up to six months in prison, but the administration has not always referred everyone caught for prosecution. Those apprehended were swiftly put into immigration proceedings and, unless they met the threshold to pursue a valid asylum claim, can be quickly deported from the country.

The current DHS plan makes no special arrangements for those who claim asylum when apprehended. While they will be allowed to pursue their claims and could eventually be found to have a legitimate right to live in the US, they could still already have a conviction for illegal entry.

BEFORE Trump- families rarely separated (and even you should realize there weren't big detention centers- because one can only imagine what republicans would have said about that under Obama.)

The rumors correctly suggested that “family detention” as a whole came before the Trump administration, but as of August 2015 intact families at the border were rarely separated. Other iterations of the rumor held that the Obama administration separated more children from their parents than the Trump administration, a claim stemming from an inaccurate retelling of the fact that an influx of unaccompanied minors from Latin America crossed the border in from 2014 onward. In those instances, minor children primarily traveled without their parents.

Claims that the “law to separate families” was passed in 1997, those claims originated with a February 2018 Department of Homeland Security statement referencing “[l]egal loopholes [that] are exploited by minors, family units, and human smugglers.” The DHS statement claimed existing immigration policies “create a pull factor that invites more illegal immigration and encourages parents to pay and entrust their children to criminal organizations.”