In the week and a half since President Biden abruptly appointed Vice President Harris to lead the effort to stem a surge of migrants at the southern border, she has plunged into a crash course on what motivates them to come illegally.

Harris is hunkering down in the White House Situation Room for briefings with experts, requesting weekend reading material, peppering advisers with questions about corruption and planning a trip to the region, according to people with knowledge of her activities. The effort is part of the administration’s larger scramble to address the record numbers of people being detained at the border.

For Harris, the past three months have been a series of firsts: The first woman to become vice president is also the first Indian American and first Black person to hold that title. Now, she is tackling her first big challenge, taking on a complex problem that has vexed Republican and Democratic administrations for decades.

At the same time, White House officials have struggled to define Harris’s directive. They have recently emphasized that her focus is on the Northern Triangle countries of Central America and the underlying causes of migration, not the more politically sensitive question of what to do with people once they arrive.

Many Democrats say this is a perilous mission for Harris, who is widely seen as a potential successor to Biden and the de facto leader of the party’s next generation. They worry it will collide with her long-term ambitions and say that, for better or for worse, she could own much of what happens on the border in coming months.

“There’s no question this one is high-risk, high-reward,” said former housing and urban development secretary Julián Castro. “I’m betting she’s more than able to get the job done.”

Harris is already dealing with competing demands. Liberal leaders and immigration activists are warning against embracing policies that are too harsh, while Republican critics are ramping up efforts to portray her and other Democrats as soft and incompetent on the border.

More than 171,000 migrants were taken into custody along the southern border in March, the highest monthly total since 2006, according to preliminary data reviewed by The Washington Post.

The new assignment for Harris — a daughter of immigrants — has been the subject of private fascination by her allies, who have traded sometimes pessimistic texts with one another about where it will lead and what it will mean for her political future, according to people with knowledge of the conversations who spoke on the condition of anonymity to describe the exchanges.

As the Biden administration struggles with a growing border crisis, long-waiting families hope their requests for asylum in the U.S. will finally be heard. (Jon Gerberg/The Washington Post)

But Harris’s friends say that she is looking for opportunities to show presidential leadership and strong support for Biden as she eyes her own future — and that her new portfolio allows her to do both. “The important thing to Kamala Harris right now is her relationship with the president of the United States. She will tell you that,” said Democratic strategist Bakari Sellers, a close Harris associate.

She has openly promoted her new role this week. On Monday, she posted a photo on Instagram of a meeting she held with administration officials who had traveled to the region. Two days later, at a roundtable discussion about coronavirus vaccines with religious leaders, Harris excused her tardiness, explaining that she had just come from a meeting with Secretary of State Antony Blinken. Harris said her chief aim is to figure out why people are fleeing their countries for the United States.

“We all know most people like being at home. They like being where they grew up,” Harris said. “. . . So we have to ask, ‘Why do people leave that?’ And usually they leave because there is a lack of opportunity or it is just not safe. And so my area of focus on the Northern Triangle is to deal with some of those issues.”

However, it is not clear the public will take such a nuanced view of her directive, Democrats say. White House officials this week have tried to stress that Harris will not be working on strategies for processing the thousands of unaccompanied children at the border.

“The vice president’s role is really focused on the Northern Triangle,” White House press secretary Jen Psaki said Friday, referring to the countries of El Salvador, Guatemala and Honduras.

The sharp increase in the numbers of migrants trekking to the border can be explained by a variety of factors, according to interviews with migrants, lawmakers on the border and experts. These include dire economic conditions in Latin America, violence and oppression, natural disasters and the pandemic, as well as Biden’s welcoming rhetoric.

The administration has recently adopted a sterner tone, warning would-be migrants not to come as officials struggle to keep up with the growing numbers of people showing up. When Biden announced Harris’s assignment on March 24, he said she would “lead our efforts” with countries that “are going to need help in stemming the movement of so many folks, stemming the migration to our southern border.”

Harris spoke with Guatemalan President Alejandro Giammattei this week, and she is expected to have more conversations with leaders in the region. Officials said she will travel to the region, though they have not yet announced a date or location for her first trip.

Biden called her the “most qualified” person for the job and cited her experience as California’s attorney general and her résumé fighting organized crime. Although Harris has experience on border issues dating to her time as attorney general, she is not seen by colleagues as an expert on Latin American geopolitics.

“The specific area is new to her,” said Ricardo Zúñiga, the State Department’s special envoy for the Northern Triangle, adding that there are a lot of nuances to the issue. “She’s very conscious of that.”

Harris’s new assignment has come with a steep learning curve. Officials at the National Security Council and the State Department said they have been briefing her in the Situation Room on Mexico and regional issues. They have presented daily memos to her and held lengthy meetings, including one session last week that went 90 minutes, according to Juan Gonzalez, the NSC’s senior director for the Western Hemisphere.

Gonzalez said Harris has responded with questions, recommendations and requests for materials to read on weekends and has been soliciting advice from members of Congress. She has spoken frequently about the need to involve the private sector in efforts to improve living conditions in the region, he said, and has taken a prosecutorial approach in pressing advisers on their plans.

“She challenged us. She asked us: ‘How do you define corruption?’ ” he recalled of a recent conversation. “ ‘Are you talking about government corruption? Are you talking about private-sector corruption? Are you talking about institutions?’ ”

Some outside allies warn that seeking to correct deeply rooted problems that have spurred people to take risky trips to the United States is not likely to lead to results in the near future.

“I think their goal is trying to foster changes and improvements in those countries. The difficulty with that goal is Rome wasn’t built in a day and you have a border crisis right now,” said Leon Fresco, an immigration attorney who was a Justice Department official in the Obama administration. “By the time you would succeed in any of those things, it would not be in any time frame to deal with what we are seeing right now.”

Biden also tasked Harris with spurring Latin American countries to tighten migration enforcement at their borders. “She’s asked a lot of questions about the migration-management component of this,” Zúñiga said.

Rep. Henry Cuellar (D-Tex.), who has been critical of the Biden administration’s response to the border surge, said that he was excited to see Harris in the new role and that it reminded him of a similar assignment President Barack Obama gave to Biden when he was vice president.

“Bottom line: We can play defense on the 1-yard line, called the U.S.-Mexico border, or we can play defense on the 20-yard line,” Cuellar said.

Like many Democrats, Cuellar said Harris — who also has been tasked with helping to sell Biden’s coronavirus relief plan and working to overcome vaccine hesitancy — is putting her political future on the line in assuming such a weighty job.

“Is there a political risk? Absolutely,” Cuellar said. “She’s got to deal with the people on the progressive [side]. She’s got to deal with people on the right.”

Recent history shows the difficulty of navigating these pressures. Many immigration activists still refer to Obama as the “deporter in chief” because of his aggressive deportation policies. The anger was still fresh in the 2020 campaign, prompting Biden to make a rare break from Obama, saying his policies were a mistake.

Republicans have been quick to pounce on Biden’s announcement of Harris’s assignment, pointing to liberal positions she has taken on immigration in the past and seeking to use the decision to attack Democratic candidates ahead of the midterm elections.

“Now that President Biden has named you Border Czar in charge of the administration's response, I want to express to you the threats and challenges caused by this administration’s open border policies,” Texas Gov. Greg Abbott (R) wrote in a letter to Harris this week.

Sellers said that Harris allies who worry about the political fallout are underestimating her abilities. But the magnitude of the challenge she faces will be unlike anything she has tackled before, he added.

“This issue is like, this is the big leagues,” Sellers said, “everything you’ve been preparing for, your leadership up to this point.”