Democrats are expected to grill Homeland Security Secretary Kirstjen Nielsen during the House Homeland Security Committee hearing Wednesday about President Donald Trump’s immigration and border security policies. It is the first time Nielsen has appeared before the Democratically controlled House.

Trump’s decision to declare a national emergency to reallocate more than $6 billion from other departments to construct a border wall will likely take center stage. Senators are poised to vote soon on a resolution to block the national emergency, following the House’s vote last week to block Trump’s emergency declaration.

In December, Trump secured $1.375 billion for 55 miles of barriers along the U.S.-Mexico border in the fiscal 2019 spending bill for the Department of Homeland Security, which is less than the $5.7 billion he requested. He later declared a national emergency to access more funds from the Pentagon and the Treasury to build the border wall. Shortly after, the House passed a resolution, which was supported by 13 House Republicans, to block the national emergency.

Nielsen has vociferously supported Trump’s decision to declare a national emergency.

“Time and again, Congress has failed to fully fund DHS to confront this situation and to handle the influx of aliens, drugs, and other illicit traffic into our country,” she said in a statement last month. “That is why I strongly support the President’s decision to unlock additional funding for physical barriers, including resources from the Department of Treasury and the Department of Defense.”

Many Democrats will likely raise concerns about the Trump administration plans to expand the policy that now requires asylum seekers to wait in Mexico while their immigration cases are being processed in the United States. Under the policy, asylum seekers will not have access to an attorney during their asylum interview.

The Trump administration began implementing the “remain in Mexico” policy, formally known as Migration Protection Protocols, in January in the San Diego area because of the large influx of Central American migrants making their way to the U.S.-Mexico border to seek asylum.

Customs and Border Protection officials told reporters last week that the administration wants to expand the program to multiple cities on the southwest border but did not say which cities they were considering.

Last week, advocacy groups called on DHS to end the policy, saying that it is putting thousands of lives in danger.

“Requiring asylum seekers to wait in Mexico while their cases are processed puts them at risk of the very harm they are fleeing, as well as new dangers. Since July 2017, the dangers facing refugees and migrants in Mexico have escalated. Asylum seekers forced to return to Mexico face risk of homelessness, malnourishment, disease, assault, kidnapping and death,” more than 500 interfaith organizations wrote in a letter to Nielsen.

Nielsen will also have to answer more questions about the treatment of detainees and if they have proper access to medical care after two migrant children died in CBP custody in December. DHS is still investigating the actual cause of death of the children.

CBP Commissioner Kevin McAleenan said he has implemented protocols that would require all children to be screened for health issues when they are taken into CBP custody.

The hearing comes a day after CBP announced that 76,103 people were apprehended at the border in February, which included individuals who were deemed “inadmissible” or caught entering the U.S. illegally. That’s the highest number of border apprehensions for the month of February since 2007. Within that figure were 36,174 family units and 6,825 unaccompanied minors. The number of family units and minors apprehended in February is a significant increase from January when 24,189 family units and 5,119 unaccompanied minors were apprehended at the border.

McAleenan said at press conference Tuesday that the high numbers of border apprehensions represent a “border security and humanitarian crisis.”

“It should be very clear from these numbers that we are facing alarming trends and rising volumes of people illegally crossing our southwest border or arriving at our Ports of Entry without documents,” McAleenan said.

Committee Chairman Bennie Thompson, D-Miss., has been highly critical of Trump’s immigration policies and of Nielsen.

“Squandering American taxpayer money on a wall may satisfy a segment of the President’s political supporters, but it will not solve the real border security challenges facing our Nation,” he wrote in a letter to Nielsen in January, when he asked her to testify before the committee.

Also on Wednesday, the House Judiciary Committee will hold a hearing on two immigration programs affecting hundreds of thousands of immigrants living in the United States with temporary resident status — those in the Temporary Protected Status and Deferred Action for Childhood Arrival programs. TPS recipients and DACA recipients, also known as Dreamers, are expected to testify at the hearing in addition to Bishop Mario Dorsonville, an auxiliary bishop for the Archdiocese of Washington, and Andrew R. Arthur, a resident Fellow at the Center for Immigration Studies, a group that advocates for lower levels of immigration.