President Joe Biden plans to announce nominations for two key immigration jobs as the administration confronts a historic influx of migrants on the U.S.-Mexico border, the White House announced on Monday.

Biden has selected Chris Magnus, the police chief from Tucson, Ariz., to lead U.S. Customs and Border Protection. He’d been a critic of the Trump administration’s anti-immigration policies.

Biden also intends to nominate Ur Jaddou, an immigrant-rights advocate who was also a critic of former President Donald Trump’s policies, to lead U.S. Citizenship and Immigration Services. The agency will implement Biden’s rollback of some of Trump’s hard-line visa policies.

If confirmed by the Senate, Magnus would help lead the response to an influx of migrants at the southern border that has posed an early challenge to Biden. The U.S. in March saw the highest number of apprehensions at the border in almost two decades, including a record number of children and teens traveling alone.

Magnus joins five other nominees at the Department of Homeland Security.

“They are highly-regarded and accomplished professionals with deep experience in their respective fields,” Homeland Security Secretary Alejandro Mayorkas said in a statement. “Together they will help advance the Department of Homeland Security’s mission to ensure the safety and security of the American people.”

The nominations announced on Monday also include top officials at DHS headquarters, jobs that had been hollowed out and led by acting leaders during Trump’s presidency. The officials would work under Mayorkas on issues ranging from immigration to cyber threats.

John Tien, the National Security Council director for Afghanistan and Pakistan under President Barack Obama, will be nominated as deputy secretary. Tien has been a managing director at Citigroup Inc. since 2011. Another former Obama administration official, Jonathan Meyer, was picked as general counsel.

The nominations also included top cybersecurity officials, a sign the issue will be a top priority for the administration. Jen Easterly, head of resilience at Morgan Stanley and a former National Security Agency official, will be nominated to lead the Cybersecurity and Infrastructure Security Agency.

Rob Silvers will be Biden’s pick as DHS undersecretary for policy. Silvers was assistant secretary for cybersecurity under Obama.

The lack of permanent leaders in top positions has threatened to hamper the Biden administration’s response to the migration crisis. With acting officials in place at key immigration agencies, getting buy-in on policy changes from rank-and-file employees is more difficult and Mayorkas was forced to take on more tasks that agency heads might otherwise handle, according to former DHS officials.

Biden still has not nominated a director for Immigration and Customs Enforcement, which apprehends and deports immigrants living illegally in the U.S. and investigates drug and human trafficking. That agency was led by acting directors for the entirety of Trump’s presidency.

The leaders Biden selected would help implement his vision for a more humane and welcoming immigration system. But Magnus and others could face tough confirmation battles in the Senate, where Republicans have blamed the president’s rhetoric for the spike in migrants arriving at the border.

If confirmed, Magnus would face a difficult challenge of how to handle the record-high numbers of border crossings that are expected to increase during the spring months. CBP has struggled to move thousands of children from cramped holding facilities to shelters within the three-day limit required by law.

The Department of Health and Human Services announced the opening of another temporary housing facility for unaccompanied minors in Michigan, bringing the total number of sites around the country to 12. Tyler Moran, a top immigration official on the White House Domestic Policy Council, said earlier Monday on MSNBC that the U.S. had reached agreements with Mexico, Guatemala and Honduras to put troops on their borders to stop migrants from coming.

Magnus will also face pressure from Democrats in Congress and immigrant-rights group to crack down on border agents who hold extreme views. Rep. Alexandria Ocasio-Cortez, D-N.Y., pressed the Trump administration in 2019 amid reports that current and former agents belonged to a Facebook group that made racist and sexist comments about migrants and Latina lawmakers.

In Tucson, Magnus developed a reputation as a progressive leader who implemented community policing practices. An outsider to DHS, Biden chose him because of his experience in dealing with immigration issues while leading a police department close to the southwest border as well as his willingness to tackle policing reforms, according to a White House official.

Magnus in 2017 wrote a New York Times op-ed criticizing Trump and Attorney General Jeff Sessions’ effort to crack down on so-called sanctuary cities for hurting his efforts to fight crime.

“The harsh anti-immigrant rhetoric and Mr. Sessions’s reckless policies ignore a basic reality known by most good cops and prosecutors: If people are afraid of the police, if they fear they may become separated from their families or harshly interrogated based on their immigration status, they won’t report crimes or come forward as witnesses,” Magnus wrote.

Before being picked to lead USCIS, Jaddou worked at watchdog arm of the liberal immigrant-rights group America’s Voice. She also led the DHS review team for Biden’s transition and was USCIS chief counsel under Obama.

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