MEXICO CITY (AP) — Vice President Kamala Harris is closing out her first foreign trip Tuesday with a visit to Mexico and a meeting with President Andres Manuel Lopez Obrador, a key but complicated ally in the Biden administration’s efforts to curb the spike in migration at the U.S. border.

While Lopez Obrador committed in a previous virtual meeting with Harris that the U.S. can “count on us” to help address the issue of irregular migration, the Mexican president has in the past blamed President Joe Biden for the increase in migration at the border. And he was chummy with his predecessor, President Donald Trump, despite Trump’s hardline polcies towards migrants.

Early last month, he also accused the U.S. of violating Mexico’s sovereignty for giving money to non-governmental organizations that were critical of his government.

But Harris, in her role dealing with the root causes of increased migration from the Northern Triangle countries of Guatemala, El Salvador and Honduras, as well as Mexico, has sought to strengthen diplomatic relations with the Mexican president. She’s held multiple phone calls and a virtual bilateral meeting with him, and Tuesday will provide the latest indication of whether her efforts will bear fruit for either nation.

“We have a partnership, a longstanding partnership. Other than Canada, we are the closest neighbors to each other,” Harris told reporters Monday night. “That is the basis of the conversation I will have with him — is with that spirit, that we have to be partners.”

The meeting follows Harris' Monday visit to Guatemala, where she met with President Alejandro Giammattei. To coincide with their meeting the Biden administration announced a number of new commitments to combat trafficking, smuggling, and corruption, as well as investments in economic development in the country. But on Tuesday, her meeting with Lopez Obrador isn’t expected to deliver as many concrete commitments.

The two will witness the signing of a memorandum of understanding that will establish greater cooperation between the two nations on development programs in Guatemala, El Salvador and Honduras. Harris aides say they’ll discuss vaccine sharing, the economic and security relationship between the two nations, and dealing with the root causes of migration from other countries in the region. Harris speaks frequently of the need to improve economic conditions for residents of the region, so they don’t feel compelled to make the trek to the U.S. border.

The memorandum of understanding, according to special envoy Ricardo Zuniga, who traveled with Harris on the trip, marks a new level of cooperation, and is important because the two nations have “some of the same issues” when it comes to irregular migration.

“It’s very important to show that the United States and Mexico are collaborating and trying to improve conditions on the ground among our neighbors, because of the importance that other countries in Central America have for both of us,” he told reporters traveling with Harris.

Harris will spend the rest of the day meeting with female entrepreneurs and labor leaders in the nation.

The meeting comes just days after the country’s midterm elections, during which Lopez Obrador’s party appeared poised to maintain their majority in Mexico’s lower chamber of the congress, but fell short of a two-thirds majority as some voters boosted the struggling opposition, according to initial election results.

Harris is not expected to address the election results during her meeting with the president, but the bloody campaign — nearly three-dozen candidates or pre-candidates were killed as drug cartels sought to protect their interests — are certain to loom over their conversations. The government’s inability to provide security in parts of the country is of interest to the U.S. in an immigration context, both for the people who are displaced by violence and the impact it has on a severely weakened economy trying to reemerge from the pandemic.

Still, while aides say corruption was a central focus of her meeting with Giammattei, it’s unclear whether she’ll raise the issue with Lopez Obrador.

But the increase in migration at the border has become one of the major challenges confronting Biden in the early months of his first term, with Republicans seizing on an issue they see as politically advantageous as polling suggests Americans are less favorable towards Biden’s approach to immigration than they are towards his policies on the economy and the COVID-19 pandemic.

They’ve tried to make Harris the face of that immigration policy, charging she and Biden are ignoring the issue because both have yet to visit the southern border. Harris told reporters Monday in Guatemala that she was focused on addressing the root causes of migration in a way that delivers “tangible” results “as opposed to grand gestures.”

Regardless of the eventual outcome of her meetings Tuesday, Mexico will remain a key partner in enforcement efforts at the border.

llegal border crossings have increased steadily since April 2020, after Trump introduced pandemic-related powers to deny migrants the opportunity to seek asylum, but further accelerated under Biden, who quickly scrapped many of Trump’s hardline border policies — most notably the “Remain in Mexico” program to make asylum-seekers wait in Mexico for court dates in U.S. immigration court.

Shortly after taking office, Biden also exempted unaccompanied children from Title 42, named for a section of an obscure 1944 public health law that allows authorities to deny entry to prevent the spread of disease. Mexico agreed to take back its own citizens under Title 42 authorities, as well as people from Guatemala, Honduras and El Salvador.

U.S. border authorities encountered nearly 19,000 unaccompanied children in March, the highest on record. Overall, it had more than 170,000 encounters on the border in April, the highest level in more than 20 years though the numbers aren’t directly comparable because getting stopped under pandemic-related authorities carries no legal consequences, resulting in many repeat crossings.

Mexicans accounted for 36% of encounters with people who crossed illegally in April, the largest nationality according to the latest monthly data available from U.S. Customs and Border Protection. Hondurans were second with 22% and Guatemalans were third with 17%.

In March, Lopez Obrador also blamed Biden for the increase in migration at the U.S. border, charging in a March press conference that the Biden administration had created “expectations” that “there would be a better treatment of migrants.”

“And this has caused Central American migrants, and also from our country, wanting to cross the border thinking that it is easier to do so,” he said.