This March 20, 2021, photo provided by the Office of Rep. Henry Cuellar, D-Texas, shows detainees in a Customs and Border Protection (CBP) temporary overflow facility in Donna, Texas. President Joe Biden’s administration faces mounting criticism for refusing to allow outside observers into facilities where it is detaining thousands of immigrant children. Photo courtesy of the Office of Rep. Henry Cuellar via AP

WASHINGTON — Shortly before Christmas last year, Susan Rice and Jake Sullivan, two top advisers to President-elect Joe Biden, sat for an interview with EFE, a Spanish wire service, to issue a stark warning to migrants considering journeying north to the nation’s southern border: Don’t come now — but help is on the way.

The next day, Biden was similarly pointed, saying his administration — while eager to roll back Donald Trump’s immigration policies — first needed to implement “guardrails” to avoid winding up with “2 million people on our border.”

Less than a month later, the new president began tearing down some of the guardrails himself. He issued five immigration executive orders on Inauguration Day alone and promised an immigration policy far more humane and welcoming than that of his predecessor. His administration also began allowing unaccompanied minors into the country, a marked departure from the Trump administration.

Now, the Biden administration is scrambling to control the biggest surge in 20 years, with the nation on pace for as many as 2 million migrants at the southern border this year — the outcome Biden said he wanted to avoid.

Along with the existing struggle to combat the coronavirus, immigration has emerged as one of the administration’s most urgent challenges — seized on by Republicans as a political cudgel, posing risks to Democrats in the 2022 midterms and potentially undermining Biden’s governing agenda. The issue also threatens to overshadow the president’s recent political victories in passing a $1.9 trillion covid relief package and making rapid strides in vaccination efforts.

The situation at the border — which Biden and his advisers steadfastly refuse to call a crisis — is the result of an administration that was forewarned of the coming surge, yet still ill-prepared and lacking the capacity to deal with it. Administration officials have been plagued by muddled messaging, sometimes making appeals that seem directed more at liberal activists than the migrants they need to dissuade from coming to the country.

The administration also took several steps — including allowing unaccompanied minors into the country — that increased the flow of migrants and encouraged more to try their luck. There are currently more than 10,000 unaccompanied migrant children in the care of Health and Human Services, and 5,000 more in the care of Customs and Border Protection, nearly twice the previous record, according to the latest figures obtained by The Washington Post.

“When you create a system that incentivizes people to come across, and they are released, that immediately sends a message to Central America that if you come across you can stay,” said Democratic Rep. Vicente Gonzalez, whose South Texas district sits near the border with Mexico. “It incentivizes droves of people to come, and the only way to slow it down is by changing policy at our doorstep. If they don’t change the policy, the flow of continued migration traffic isn’t going to stop or slow down.”

Some of the factors facing Biden and his team are outside of their control, from deteriorating conditions in Central America to the increasing flow of migrants that had already been happening in Trump’s final months. Under a Trump-era public health order known as Title 42, the Biden administration had been rapidly expelling border-crossers to Mexico. But in late January, Mexican authorities stopped taking back some of the families — a step that forced U.S. border agents to accept parents with children under 7, further exacerbating the influx.

In an ABC News interview last week, Biden disputed the notion that asylum seekers were surging to the border because they had heard he was “a nice guy,” and reiterated his administration’s appeal that they stay home. “Yes, I can say quite clearly: Don’t come over,” he said. “Don’t leave your town or city or community.”

Administration officials said many of their actions have been based on a desire to undo what they say were Trump’s illegal policies, as well as to take a more compassionate approach to migrants, especially children and families. Many of their initial moves were focused on interior enforcement and not at the border, one official added. There were no good options, they argued, but continuing to enforce Trump-era policies was simply antithetical to what the Biden administration stands for.

“We made the choice that we don’t want to be an administration that — if we can help it — has to turn back kids,” Rice, Biden’s domestic policy adviser, said in an interview. “We’re basically having to build the plane as we’re flying.”

The warnings began before Biden even took office.

During the transition period, career officials at U.S. Customs and Border Protection tried to issue sober alarms to the Biden team about the likelihood of a crisis at the border that could quickly overwhelm the nation’s capacity. Senior CBP officials delivered Zoom briefings to the Biden transition team that included modeling projections showing a steep increase in the arrival of unaccompanied minors if Trump’s policies were suddenly lifted, according to one current and two former Department of Homeland Security officials.

Chad Wolf, the acting DHS secretary at that time, did not participate in the meetings, but said he talked to transition officials about the risks they faced, and that career officials — not polarizing Trump appointees — briefed the Biden team to help underscore the legitimacy of the crisis.

“It’s one thing to hear it from political appointees, but career folks were telling them the same thing. They should have been better prepared,” Wolf said. “And I know they were briefed in detail by CBP.”

Biden transition officials understood the risks, as well, identifying a surge of unaccompanied minors and a dearth of shelter space exacerbated by covid as the most pressing problems.

Yet Biden immediately embarked on an aggressive strategy to roll back Trump administration policies. On his first day, Biden suspended border wall construction, affirmed protections for young immigrant “Dreamers,” scrapped Trump’s ban on travel from seven majority-Muslim countries, and ordered a 100-day moratorium on deportations by U.S. Immigration and Customs Enforcement. He also sent a broad immigration overhaul proposal to Congress, including an eight-year pathway to citizenship for immigrants without legal status.

More moves followed in rapid-fire succession. The president ordered a major increase in refugee admissions. He launched a task force to reunify families separated by Trump’s “Zero Tolerance” crackdown while easing restrictions for minors under Title 42. And he ended the “Remain in Mexico” program Trump had used to send asylum seekers back across the border to wait outside U.S. territory for their cases to be decided — allowing hundreds of families crowded into squalid camps to enter the United States, producing emotional scenes that circulated widely in Spanish-language media.

According to Biden administration officials, Trump had left them with a rickety immigration system at best — a patchwork of deterrent policies, some with dubious legal underpinnings — because his only goal was to keep people out.

But Biden did not have adequate preparations in place when he began rolling back some of Trump’s policies and sounding a welcoming note. Even some Biden allies said they had expected the White House to use the coronavirus crisis to buy themselves time to implement a more robust immigration plan before beginning wholesale policy changes, and were taken aback when Biden forged ahead.

DHS Secretary Alejandro Mayorkas acknowledged last week that the Biden administration is “on pace to encounter more individuals on the southwest border than we have in the last 20 years.” The latest CBP enforcement data shows agents made nearly 100,000 arrests and detentions so far in March, on pace to be the highest one-month total since 2006. On March 10, the busiest day yet, agents took more than 6,200 into custody.

“No end in sight,” the Border Patrol’s chief in the Rio Grande Valley sector wrote on Twitter this week, sharing images of large groups of families and small children arriving across the river.

On Friday, Sen. Chris Murphy, D-Conn., joined Mayorkas and three other lawmakers, including two Republicans, on a trip to the border. Leaving a processing facility in El Paso, Murphy tweeted that he was shaken by what he saw.

“100s of kids packed into big open rooms,” wrote Murphy. “In a corner, I fought back tears as a 13 yr old girl sobbed uncontrollably explaining thru a translator how terrified she was, having been separated from her grandmother and without her parents.”

A U.S. Customs and Border Protection agent looks on near a gate on the U.S.-Mexico border wall as agents take migrants into custody, Sunday, March 21, 2021, in Abram-Perezville, Texas. The fate of thousands of migrant families who have recently arrived at the Mexico border is being decided by a mysterious new system under President Joe Biden. U.S. authorities are releasing migrants with “acute vulnerabilities” and allowing them to pursue asylum. But it’s not clear why some are considered vulnerable and not others. Julio Cortez/AP photo

It was late January, just a few days into Biden’s presidency, when Rep. Henry Cuellar, D-Texas, started getting worried, calling a White House contact to discuss the surge of migrants arriving on the southern border.

“I said, ‘Hey, I just want to let you know what’s going on. We need to get a handle on this before it gets out of hand,'” he recalled saying. “Even within a week, I was already calling the White House to say, ‘Hey guys, you’ve got to take a look at it.’ ”

In the months that followed, Cuellar, the son of migrant farmworkers, grew increasingly frustrated, feeling that not only had administration officials failed to heed his warnings, but they were uninterested in the advice of local officials like himself who had a close-up view of the problems.

His anger reached a boiling point in early March when the White House quietly sent a delegation of officials — led by Rice — to visit South Texas tent sites badly overcrowded with teens and children, without giving a heads up to him, Gonzales or Rep. Filemon Vela, all Democrats who represent Texas border districts.

“You would assume they would give us the courtesy,” Cuellar said. “I mean, they were in Laredo, about six or seven minutes from my house.”

Several White House officials dismissed the criticisms, saying the visit was a narrowly targeted fact-finding mission.

Administration officials briefed Biden after the trip, showing him photos from the visit. He also receives updates several times a week on the border situation, White House press secretary Jen Psaki told reporters.

Republicans are reveling in the administration’s border problems. Speaking on the Senate floor Thursday, Minority Leader Mitch McConnell (R-Ky.) referred to the decision to direct the Federal Emergency Management Agency to help with surge of migrants as a way to mock the administration’s refusal to call it a crisis.

“So either this is the first time FEMA has been deployed just to admire a situation that is going smoothly, or the administration is not being straight with the American people,” McConnell said.

A migrant carries a child as their group follows an official to an intake area after turning themselves in upon crossing the U.S.-Mexico border, early Wednesday, March 24, 2021, in Roma, Texas. A surge of migrants on the Southwest border has the Biden administration on the defensive. The head of Homeland Security acknowledged the severity of the problem but insisted it’s under control and said he won’t revive a Trump-era practice of immediately expelling teens and children. Julio Cortez/ AP Photo

On Thursday, the Biden administration and Mexico reached an agreement: The United States agreed to supply Mexico with excess doses of the AstraZeneca coronavirus vaccine, and Mexico pledged to help the United States better contain the migration surge, including taking back more Central American families expelled under the Title 42 emergency health order. Mexican authorities also announced the closure of the country’s southern border to nonessential travel.

The deal with Mexico is among the first steps the administration has taken aimed at slowing the crossings. Most of its other measures have sought to add capacity for unaccompanied minors and accelerate the release of family groups. Homeland Security officials are also considering flying migrants to states near the Canadian border for processing, according to two DHS officials and an email reviewed by The Post.

Ultimately, solving the nation’s immigration crisis will involve addressing the root causes, likely with a broad legislative solution that will take time, administration officials say. But right now, two key goals are getting migrant children out of CBP care and placing them with vetted family members and sponsors in the United States.

More than 500 teens and children are arriving each day without parents, at nearly three times the rate they are being released, the latest HHS figures show.

This challenge is further complicated by the pandemic, which has limited shelter space and further slowed down the process. But officials point to steps they have taken so far to help expedite the process.

Rep. Veronica Escobar, D-Texas, a vocal Biden defender, said the administration made the right call morally by exempting unaccompanied children from expulsion, calling it “a horrific thought.”

The Biden administration’s scramble to add shelter capacity to house and care for these children, Escobar said, is partly the result of the Trump administration’s chaotic handoff.

“Were they unprepared? Well, yeah, because there was no transition,” Escobar said. “The transition was an insurrection.”

Several administration officials have also argued that immigration surges are cyclical, and this current one would likely have occurred regardless of who was president.

“The administration has done everything it possibly could to be prepared,” said Tyler Moran, a top Biden immigration adviser. “We have to stop thinking there’s this tension between having a well-managed border and a humane immigration policy.”

White House press secretary Jen Psaki speaks with reporters in the James Brady Press Briefing Room at the White House, Friday, March 12, 2021, in Washington. Alex Brandon/AP Photo

In her White House briefing March 18, answering a question on immigration, Psaki seemed to slip up, referring to “the crisis on the border.”

Pressed later on her word choice, Psaki corrected herself, saying “challenges on the border,” and replied that her earlier misstatement did not reflect any change in the administration’s thinking about the border surge.

The misstep underscores the administration’s struggle to send a coherent message on the border. Despite repeatedly saying that now is not the time for asylum seekers to come, officials are still losing the messaging war: Smugglers, as well as relatives of the migrants already in the United States, often argue that Biden and his more lenient policies mean making the journey now is worth the risk.

Cuellar said that Biden and other officials were sending “a terrible message” with their initial pitch to migrants not to come now — while seeming to suggest they can still come later.

Biden has long struggled to be an effective messenger on immigration. A confidential memo produced last spring by Cristóbal Alex, a senior campaign adviser who now serves as White House deputy Cabinet secretary, blamed “our own uneven immigration messaging” and anger with President Barack Obama’s aggressive deportation policies for fueling Biden’s struggles competing for Latino voters against Sen. Bernie Sanders, I-Vt., in the primary, according to a person with knowledge of the document.

On March 17, White House officials convened a private video call with Democratic strategists and prominent voices on immigration to coordinate their messaging. The officials talked about the need to push back against Republican attacks on the topic, and stressed key talking points — that immigration trends are cyclical and that Trump’s mishandling of the system made the challenges for Biden even harder, according to three people on the call who spoke on the condition of anonymity to reveal internal discussions.

White House communications director Kate Bedingfield also argued that the immediate crises at hand are the coronavirus pandemic and the economy, and that Republicans are trying to use immigration to distract from the covid relief package’s popularity, one of the people on the call said.

In the meantime, one clear message has resonated with migrants. The week after Rice’s border visit, Cuellar visited a detention facility for migrant children in Carrizo Springs, Tex. Cuellar said he asked 16 — and 17-year-olds whether they had heard Biden when he said not to come to the United States.

The teenagers looked at each other and said no, he recalled. Okay, Cuellar pressed, what about the messages from friends, neighbors and family saying now is the time to come — were they hearing those?

“They all raised their hands and said yes,” Cuellar recalled. “They said, ‘We see this on TV. We see images of people coming across. . . . We see people coming across, so we’re going to do the same thing.'”

“This,” the migrants told him, “is our opportunity to do this.”