You've likely seen heart-wrenching coverage of migrant youngsters streaming across the Mexican border into Texas, Arizona, New Mexico and California. Now wrap your brain around these astonishing numbers: In March, the U.S. government picked up nearly 19,000 children traveling alone across the southern border, the largest monthly total ever recorded. (February's total was near 9,300, by comparison, and January's was below 5,700.) As of last week, 20,273 teens and younger refugees were in the custody of two federal agencies, which try to reunite them with relatives who came earlier or place them in emergency shelters and foster care. A lack of shelter space leaves unaccompanied children in overcrowded and ill-suited Border Patrol facilities.

Adults and children travel from their homelands — primarily Mexico, Honduras, Guatemala and El Salvador — for many reasons: worsened poverty and hunger due to Covid, drug-selling violence, government corruption, natural disasters, agricultural diseases or droughts. The daily flow has increased since last April, when Donald Trump was president, and now creates a major test for the new president as he reverses many of his predecessor's hardline immigration tactics.

The Biden administration is still rapidly expelling most single adults and families under a public health order issued by Trump at the start of the Covid pandemic. But it lets teens and children stay, at least temporarily, and they come in a growing wave. The White House response to the historic surge – widely called a crisis – is to seek more charity sponsors and other shelters for the minors and to increase assistance to Central American nations. The Department of Health and Human Services' refugee office is preparing to open at least 11 emergency housing sites with 18,200 beds at convention centers, work camps, a church hall and military posts in Texas and California. The federal resettlement office also increased capacity at its network of state-licensed shelters.

Texas governor says: "President Biden’s reckless open border policies are causing a surge in crossings … The Biden administration must answer for enticing unaccompanied minors into inhumane condition." – Greg Abbott, Republican

Texas congresswoman says: "We began seeing the increase in unaccompanied minors going back to last April 2020. This is not something that happened as a result of Joe Biden becoming president." – Rep. Veronica Escobar of El Paso, Democrat

Texas professor says: "Trump basically shut down our immigration system and ended the laws on the books. So there's going to be a pent-up number of people that were waiting to come, or that were en route." -- Ruth Wasem, University of Texas public policy professor