The Biden administration is searching for new ways to stem the surge in the number of migrants at the southern border, dispatching officials to Mexico and Guatemala to seek their governments’ help, sending sterner warnings to would-be migrants not to come, and devising alternative pathways to apply for legal entry without showing up in person.

The strategies, which administration officials outlined Monday, reflect the growing pressure on President Biden and his advisers to slow the increase in illegal crossings that has accelerated since he took office. Biden is navigating sometimes competing demands: pleas from border lawmakers to more aggressively dissuade would-be migrants, and exhortations from human rights advocates to treat them humanely.

The sharpest challenge is how to deal with thousands of children taken into custody under a policy of not turning away unaccompanied minors. Rep. Henry Cuellar (D-Tex.) on Monday released photographs of a temporary border tent in Donna, Tex., where children were placed in crowded areas divided by clear partitions, some huddled under foil blankets on modest bedding.

The Post’s Nick Miroff explains how the Biden administration is searching for new ways to slow the surge of unaccompanied minors along the U.S.-Mexico border. (Mahlia Posey/The Washington Post)

The photos echoed criticism faced by former president Donald Trump for his handling of children at the border, though administration officials said the current conditions are far more humane. “The system is being overwhelmed right now,” Cuellar said. “No ifs, no buts about it.”

Although the administration’s message “has been changed,” Cuellar said, with more emphasis on declaring that the border is not open, “they’ve got to do more to overcome the messages you hear in Central America” from smugglers emphasizing purportedly lax enforcement. The congressman urged the Biden team to promote images of people being turned away at the border.

Other lawmakers who have witnessed the border situation also voiced serious concerns Monday. “In general, I saw a situation that was spiraling out of control,” said Sen. Rob Portman (R-Ohio), who visited the border last week.

The administration’s search for answers comes as the border surge threatens to become an ever-greater logistical and political crisis. Biden’s team has often seemed on the defensive regarding the border, quickly relaxing some of Trump’s hard-line policies, but struggling to take control of the influx after border arrests and detentions went up to some of the highest levels in a decade at the end of the Trump presidency. Biden is likely to face an array of questions on the border at his first formal news conference on Thursday.

The Biden administration released video from inside two processing facilities in Texas where a surge of migrants, many unaccompanied minors, have arrived. (U.S. Customs and Border Protection)

During a closed-door virtual retreat with Democratic senators on Monday evening, Biden was pressed on the issue by at least one member of his own party, according to officials familiar with the discussion.

Sen. Mark Kelly (D-Ariz.) asked Biden what the administration’s timeline was for additional resources and facilities to manage the increase in the number of migrants at the border, as well as coronavirus testing protocols there.

Kelly, a border-state freshman who is likely to face a tough reelection challenge in 2022, told Biden he was concerned that the state’s resources could become strained under the migration challenges.

In response, Biden did not delve into specifics but stressed to the senators that his administration was building additional capacity to care for the migrants, and that the current challenges began under his predecessor. He did not say whether he or Vice President Harris would visit the border. The people spoke on the condition of anonymity to discuss a private meeting.

Biden on Monday dispatched a delegation led by Roberta Jacobson, his coordinator for the southwest border, to Mexico to meet with officials and “develop an effective and humane plan of action to manage migration,” according to National Security Council spokeswoman Emily Horne.

Jackson will be joined by Juan Gonzalez, the National Security Council’s senior director for the Western Hemisphere, and Ricardo Zuniga, the State Department’s special envoy to the Northern Triangle, which comprises Guatemala, Honduras and El Salvador.

After Mexico, Gonzalez and Zuniga will continue on to Guatemala, where they will talk to officials about how to expand economic opportunities in the region in an effort to give people less reason to flee to the United States, according to senior administration aides.

White House press secretary Jen Psaki told reporters the U.S. officials will explicitly ask Mexico and Guatemala to help reduce the number of migrants arriving at the border. She listed other steps the administration has taken, including airing thousands of radio and social media commercials in multiple languages in Brazil, El Salvador, Guatemala and Honduras urging people not to come to the border.

Responding to calls by lawmakers of both parties to allow reporters into facilities holding migrant children, Psaki said officials were “working to finalize details” to open them up to the news media and to hoped to “have an update in the coming days.” But she refused to label the situation a crisis, hewing to the line officials have repeatedly walked.

“Children presenting at our border who are fleeing violence, who are fleeing persecution, who are fleeing terrible situations, is not a crisis,” Psaki said. “We feel that it is our responsibility to humanely approach this circumstance and make sure they are treated with — treated and put into conditions that are safe.”

Biden, Jacobson and other officials have used sharper language in recent days to warn migrants not to come, saying flatly that they should not do so. That marks a shift from previous entreaties not to come “now,” which suggested that they could do so later.

“What we are conveying from our end is that the border is not open,” Psaki said.

The administration is also preparing to roll out additional legal pathways that would not require asylum seekers to physically present themselves at the border, according to an aide with knowledge of the plans, who spoke on the condition of anonymity to discuss an initiative that had not been formally announced.

Overall, Monday’s moves were aimed at complementing other recent actions, such as reopening a program to reunite certain children from El Salvador, Guatemala and Honduras with parents living legally in the United States.

White House officials said they were focused on two particularly pressing goals: creating more space for the children who are currently being held, and moving them swiftly into more-permanent homes.

To that end, city and county officials in San Diego announced Monday that the San Diego Convention Center would be used temporarily as a shelter for unaccompanied migrant children in the care of the Department of Health and Human Services. The convention center will be used for about three months, officials said.

“We are working closely with our federal partners to finalize the details for preparing to receive these young people and provide them with care, compassion and a safe space to transition while they are reunited with families or sponsors,” the county and city said in a joint statement.

In some circumstances, the administration appears to be struggling with transferring children from the custody of U.S. Customs and Border Protection to Health and Human Services. HHS’s Office of Refugee Resettlement is charged with providing care for unaccompanied children entering the United States, while CBP is a law enforcement agency assigned to patrol and secure the border.

The challenges were highlighted by a trip to the border taken last week by Homeland Security Secretary Alejandro Mayorkas with a bipartisan Senate delegation.

The group first toured an overcrowded CBP facility where many unaccompanied migrant children had been held for days longer than the legally mandated 72 hours. An HHS facility the group visited had just 78 children in a facility that could shelter and care for up to 500 children, with senators receiving no clear answer on why it was taking so long to transfer the children out of CBP custody when HHS facilities were readily available.

The Trump administration had been expelling migrants since March 2020 under Title 42 of the public health code, using the pandemic as a reason for refusing to let asylum seekers in the U.S. Critics accused the administration of using the coronavirus as a pretext to impose its hard-line immigration policies, and the American Civil Liberties Union has filed lawsuits seeking to halt the practice.

As the court case unfolds, Biden has voluntarily stopped sending unaccompanied minors home. But officials are still expelling thousands of migrants, including families, as the Centers for Disease Control and Prevention reviews health conditions on the border.

When senators traveling with Mayorkas last week pressed him about the future of Title 42, he expressed concern about losing the power of the emergency public health order, according to two people familiar with Mayorkas’s private remarks.

Beyond the conditions facing children being held at the border, Cuellar raised concerns about 150 migrants he said were recently released into the United States without notice to appear in court, a move that career CBP officials said had no modern precedent.

Portman, the top Republican on the Senate Homeland Security and Governmental Affairs Committee, accompanied Mayorkas on his trip, and spent time with agents who conveyed concerns that the number of migrants arriving at the border would continue to spike. Portman said in an interview that some of the administration’s countermeasures are helpful, but probably too small to make an appreciable difference anytime soon.

Biden, who has not visited the border as president, said Sunday that “at some point I will.” But White House officials played down the prospect of an imminent visit. “I don’t have any trips to preview for you,” Psaki said.

On the road in Jacksonville, Fla., to promote the $1.9 trillion pandemic relief bill Biden recently signed into law, Vice President Harris said Monday she is not planning to visit the border “today” but that she has in the past and will do so again.

And sShe reiterated the Biden position that Trump left him a tough situation at the border. “We were left with a very challenging situation. Let’s get these kids out of CBP custody and get them into HHS custody,” Harris said. “We’ve got to treat this issue in a way that is reflective of our values as Americans.”

Members of Congress will focus more attention on the migration challenges later this week as Democrats and Republicans lead various delegations down to the border. Rep. Joaquin Castro (D-Tex.) plans to lead a trip of lawmakers to visit an HHS shelter in Carrizo Springs, Tex., the first shelter for migrant children that opened under the Biden administration.

Sen. John Cornyn (R-Tex.) said he and Sen. Ted Cruz (R-Tex.) will travel to the border with more than a dozen other GOP senators later this week. Cruz sent Biden a letter Monday criticizing the administration for not allowing reporters to join him during his planned border travels.

“I just think the more people from up here go to the border see things for themselves, the better it is, because I think we’re kind of locked into competing parallel universes when it comes to what’s happening,” Cornyn said.

Cornyn teamed up with Democratic Sen. Kyrsten Sinema (D-Ariz.) to send their own letter to Biden, urging him to “use your full authorities to effectively respond to and successfully manage the ongoing crisis.”

Maria Sacchetti and Nick Miroff contributed to this report.