WASHINGTON (AP) — A delegation of White House officials and members of Congress was traveling to the southern border on Wednesday to tour a facility being used to house migrant children as increasing numbers of unaccompanied young people cross into the United States.

The visit to a facility in Carrizo Springs, Texas, comes as the Biden administration faces a growing humanitarian and political challenge at the U.S.-Mexico border that threatens to overshadow its ambitious legislative agenda.

President Joe Biden also was meeting with key Cabinet members and immigration officials on Wednesday as he faces pressure to address the situation.

More than 750 teenagers are being held at Carrizo Springs. Like other facilities operated by the Health and Human Services Department, it includes a small group of children who have tested positive for COVID-19, potentially having contracted the virus in Border Patrol custody. They are placed in isolation.

The Biden administration has in recent weeks rushed to open more sites for children operated by HHS. It announced Tuesday that it would open a second site in Carrizo Springs. The convention center in San Diego will also open to teenagers, and HHS is exploring housing teenagers at military bases in San Antonio and El Paso, Texas.

But the U.S. is exhausting capacity almost as quickly as it can add it. A week after opening, the convention center in downtown Dallas is at nearly 2,000 teenagers, just shy of its 2,300-bed capacity. Experts on child welfare say HHS must release children more quickly, particularly the estimated 40% of children in custody who have a parent in the U.S. ready to take them.

The White House was limiting media access on Wednesday’s tour, keeping it to just one TV crew.

Questions have grown about a lack of transparency at the border as the administration has stymied most efforts by outsiders to see and document the conditions. A Democratic lawmaker released photos earlier this week to show conditions at the facility and to display the extreme challenges that border agents face in watching so many children, sometimes for a week or longer despite the Border Patrol’s three-day limit on detaining minors.

With the number of migrants increasing, administration officials say Biden inherited an untenable situation that resulted from what they say was President Donald Trump’s undermining and weakening of the immigration system.

But as Congress pivots to immigration legislation, stories of unaccompanied minors and families trying to cross the border and seek asylum and of overwhelmed border facilities have begun to dominate the headlines, distracting from White House efforts to promote the recently passed $1.9 trillion COVID-19 relief bill.

Located at a converted “man camp” for oilfield workers, the Carrizo Springs site first opened to migrant teenagers briefly in 2019 during the last sharp rise in border crossings. The Biden administration re-opened it in February. It has long, narrow dormitories and classrooms set up in trailers, with a large tent that serves as a dining hall.

Officials are trying to build up capacity to care for some 14,000 migrants now in federal custody — and more likely on the way.

Since Biden’s inauguration on Jan. 20, the U.S. has seen a dramatic spike in the number of people encountered by border officials. There were 18,945 family members and 9,297 unaccompanied children encountered in February — an increase of 168% and 63%, respectively, from the month before, according to the Pew Research Center. That creates an enormous logistical challenge because children, in particular, require higher standards of care and coordination across agencies.

Among the reasons for the increase: thousands of Central American migrants already stuck at the border for months and the persistent scourge of gang violence afflicting Northern Triangle countries — Guatemala, Honduras and El Salvador.

Still, the encounters of both unaccompanied minors and families are lower than they were at various points during the Trump administration, including in spring 2019.

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