The Biden administration kept a Trump-era policy known as "Title 42" as a tool to quickly turn back adults and families who illegally cross the southern border— but new Department of Homeland Security data leaked to Axios shows in recent days it's hardly been used for families.

Driving the news: The data shows an average of just 13% of nearly 13,000 family members attempting to cross the U.S.-Mexico border were returned to Mexico between March 14 and March 21 using the public health order, which essentially says the U.S. can close the border to nonessential travel because of the coronavirus.

• It's a sign of how the administration is struggling to keep up with a migration surge, and has been recently hamstrung by Mexico's inability to take in more families the U.S. otherwise would expel.
• That doesn't mean the other 87% percent will remain in the U.S. indefinitely, but they will be allowed into the U.S. to go through immigration proceedings.
• It's too soon to say how many will be ultimately granted asylum or deported — and when. Proceedings can take years.

What they're saying: Given fluctuating migration flows, "one week of statistics doesn’t reflect the full picture," a DHS spokesperson told Axios. "Our policy remains that families are expelled, and in situations where expulsion is not possible due to Mexico’s inability to receive the families, they are placed into removal proceedings.”

• White House press secretary Jen Psaki said Monday that the process of deporting those families sometimes "takes a minute to ensure there is proper transportation and steps in place to do that."

Why it matters: Psaki said there are only "narrow, narrow circumstances in which families can't be expelled."

• But administration officials also say Mexico doesn't always have capacity to take in families sent there under Title 42 — especially when families include young children.
• A DHS official told Axios the U.S. is "working with our partners in Mexico to increase their capacity."
• Top Biden border officials met with Mexican officials on Monday to discuss solutions to the surge at the border.

When Title 42 is not invoked, these migrants are tested for the coronavirus and quarantined if needed before being placed in removal proceedings, according to the DHS official and Psaki.

• Some are transferred to the custody of Immigration and Customs Enforcement, which recently signed a contract to provide hotel rooms for migrant families.
• Some are released at bus stops or local nongovernmental organizations.
• Border patrol agents in the Rio Grande Valley sector are releasing some migrants without a court date.

The big picture: The Biden administration has taken fire from both the right and the left over its use of Title 42.

• Progressives have decried the use of the order to expel families and adults, while conservatives have blamed the rising number of unaccompanied minors on the administration's choice not to use the order to return them to Mexico.