April 1 (UPI) -- President Donald Trump took the unusual step of attending Wednesday's Supreme Court hearing on birthright citizenship, later criticizing the United States for being "stupid enough" to allow the practice.

The high court heard oral arguments in the case -- Trump vs. Barbara -- a challenge to Trump's January 2025 executive order seeking to change the application of the Citizenship Clause of the 14th Amendment, ending birthright citizenship.

By attending the hearing, Trump became the first sitting U.S. president to sit in on oral arguments before the Supreme Court. He stayed in the courtroom for about an hour to hear Solicitor General D. John Sauer defend Trump's executive order. Trump left the hearing about 15 minutes after a lawyer for the American Civili Liberties Union began its case against the order, CNBC reported.

After returning to the White House, Trump took to Truth Social to voice his opposition to birthright citizenship, which offers citizenship to the children born to immigrants in the United States in some situations.

"We are the only Country in the World STUPID enough to allow 'Birthright' Citizenship!" Trump wrote.