House Democrats are planning to subject Secretary of Homeland Security Kirstjen Nielsen to the most intense grilling of her career on Wednesday regarding a host of border security issues—including allegations that she lied to Congress about the Trump administration’s family separation policy.

According to eight senior staffers working for the House Committee on Homeland Security’s Democratic majority, Nielsen should go into the hearing expecting detailed lines of questioning on some of the Trump administration’s most controversial policies and actions, ranging from eminent domain seizures along the U.S. southern border to President Donald Trump’s “zero-tolerance” immigration policy to the deaths of migrant children in government custody, as well as the veracity of her own past statements to Congress.

“Secretary Nielsen would be wise to finally tell the truth about the Trump administration’s grotesque family separation policy,” one senior staffer in the office of a Democrat on the committee told The Daily Beast. “If she refuses to do so, Democrats on the committee won’t hesitate to call her a liar.”

The staffer added that they expect Democrats on the committee to warn Nielsen against committing perjury, “but ultimately that is a question for prosecutors.”

Nielsen has been dogged for months by allegations that she lied to Congress about plans to separate undocumented children from their parents at the U.S.-Mexico border, after Sen. Jeff Merkley (D-OR) released a leaked memo detailing the Department of Homeland Security’s attempts to craft a policy to “separate family units” as early as December 2017. Nielsen, speaking before the House Judiciary Committee more than a year later, told then-Rep. Luis Gutierrez (D-IL) that characterizing her longtime denial that a family separation policy ever existed “is fighting words.”

“I’m not a liar—we’ve never had a policy for family separation,” Nielsen responded under oath. Nielsen also told the Senate Homeland Security and Governmental Affairs Committee last May that she had “not been directed to [separate migrant parents from children] for purposes of deterrence,” even though the 2017 plan noted that such a policy would have “a substantial deterrent effect” on illegal immigration.

The memo, Merkley said at the time of its release, proved that Nielsen lied in her testimony. “Secretary Nielsen and the administration lied. Period,” Merkley tweeted. “We have proof that the Trump War on Migrant Children was carefully constructed to inflict harm on children and create a humanitarian crisis.” Merkley has since requested that FBI Director Christopher Wray open an investigation into whether Nielsen committed perjury.

Rep. Emanuel Cleaver II (D-MO) told The Daily Beast that when it comes to Nielsen’s denials about family separation, patience among Democratic members of the committee has worn thin.

“There is absolutely no law that requires family separation; it was a policy proactively pursued by DHS and one in which the agency was woefully unprepared to implement,” Cleaver said.

“That will come up,” a senior staffer on the committee told The Daily Beast. “She has been asked on this before of course and has pushed back… but she has not been before Congress since December, and, of course, the Merkley memo came out after this.”

Nielsen’s testimony in the committee hearing—one of four scheduled on the subject of immigration on Wednesday—will be her first appearance in front of the Democratic majority in the House of Representatives, and follows months of increasingly exasperated invitations to testify by Rep. Bennie G. Thompson (D-MS), chair of the House Committee on Homeland Security.

In a January letter requesting that the secretary’s office provide the committee with a host of documents relating to the construction of a border wall, family separation, and the treatment of children in U.S. Customs and Border Protection facilities, Thompson derided a presentation Nielsen submitted to Congress as full of “misinformation and outright lies,” used to make the case for Trump’s “boondoggle border wall.” After Nielsen refused Thompson’s first invitation to testify in February, citing a then-impending government shutdown, the chair blasted the decision as “outrageous” and publicly floated issuing a subpoena to compel her appearance.

“If she says she’s not coming, we’ll subpoena her to the committee,” Thompson told the Washington Post at the time. “We need to hear from her. If border security is important, we need to hear her vision.”

The Department of Homeland Security did not respond to questions regarding Nielsen’s testimony or potential answers to questions regarding the Merkley memo, but tensions between Nielsen and the committee appear set to reach a crescendo.

In addition to questions about the Merkley memo and family separations, members have a host of potentially uncomfortable inquiries planned. Rep. Val Demings (D-FL), who recently introduced a bill to protect landowners from eminent domain seizures along the border, will likely ask Nielsen why ranchers should be forced to give up their land for a barrier they don’t want, said Demings’ communications director Daniel Gleick. The office of Rep. Nanette Diaz Barragán (D-CA) told The Daily Beast that the onetime attorney for asylum seekers will focus on the so-called “metering” of those seeking asylum in the United States.

Rep. Bonnie Watson Coleman (D-N.J.) is looking to her district for lines of inquiry to pursue, said communications director Courtney Cochran, and hopes to press Nielsen on the death of Mariee Juárez, a 19-month-old girl who died after contracting a respiratory illness while in the custody of U.S. Immigration and Customs Enforcement and whose family lives in her district.

At least three members of the committee—Reps. Cleaver, Max Rose (D-NY) and Jose Luis Correa (D-CA)—are shaping questions about the Trump administration’s misleading insistence that opioids, weapons, and terrorists are being smuggled across unguarded sections of the U.S. border.

With a full plate of aggressive questions, some posed by Democrats who have publicly called on Nielsen to resign, Nielsen’s testimony could be critical to keeping her on the president’s good side. Although reports that the secretary is on the outs with the mercurial Trump have quieted in recent months, the president has been quick to blame Nielsen for failing to implement his more draconian immigration proposals. In November, Trump told Fox News that Nielsen had to “get much tougher” if she wished to remain in her position, a difficult needle to thread in the face of a hostile Democratic committee.

“My colleagues and I have been wanting for several months to hear directly from the Secretary about the president’s border ‘emergency’ declaration and other border security policies,” Cleaver said.