Supreme Court oral arguments in a key immigration case grew heated Tuesday as Justice Ketanji Brown Jackson, President Biden’s first nominee to the court, rejected the White House’s interpretation of federal law.

Jackson accused Solicitor General Elizabeth Prelogar of having a “conceptual problem” in her understanding of the Administrative Procedure Act, which requires the federal bureaucracy to take certain steps when changing policies.

The case, brought by Texas and Louisiana, challenges Homeland Security Secretary Alejandro Mayorkas’ 2021 memo that said federal agents should review the “totality” of an illegal immigrant’s threat to public safety rather than automatically expel them for certain crimes for which a 1996 law says they “shall” be detained.

The underlying legal dispute is complex and the outcome would bear on only about 60,000 to 80,000 illegal immigrants who are also criminals, Texas Solicitor General Judd Stone acknowledged to justices — but a rebuke of the memo would be a black eye politically for Biden and potentially would allow states more avenues to enforce immigration law, which historically has been done at federal discretion.