The Supreme Court slapped down President Donald Trump's attempt to end birthright citizenship in a major blow to the administration's radical vision for the composition of the country.In a landmark 6-3 decision, the Justices halted the President's attempt to end birthright citizenship - calling it blatantly unconstitutional and out of bounds. The constitutional guarantee was enshrined by the 14th Amendment, and ratified in 1868 to guarantee citizenship to freed slaves, but has since applied to every person born on US soil or its territories.It impacts an estimated 150,000 children born in the US annually to noncitizens. The ruling is a major defeat for Trump, and comes as the high court has ruled against him in a handful of major cases – including invalidating his sweeping tariff regime, and blocking his effort to fire Lisa Cook from the Fed's board of governors. Trump first tried to end birthright citizenship by executive order on Inauguration Day 2025 - a move subsequently struck down by lower courts as unconstitutional.'Citizenship, then and now,' conservative Chief Justice John Roberts said, writing for the majority, 'was the right to have rights... to freely participate in our political community.''The Framers of the Fourteenth Amendment extended that promise to ''every free-born person in this land,' Roberts added. 'We keep that promise today.' Birthright citizenship was enshrined by the 14th Amendment, and ratified in 1868 to guarantee citizenship to freed slaves, but has since applied to every person born on US soil or its territoriesRoberts was joined by Trump-appointed Amy Coney Barrett and liberal Justices Sonia Sotomayor, Elena Kagan, and Ketanji Brown Jackson in the majority. Conservative Justice Brett Kavanaugh joined the majority in part but dissented in part. The stakes in the case were momentous, and put Supreme Court precedent on a collision course with the expansion of executive power. The President made history in April by becoming the first sitting president to attend Supreme Court oral arguments in person - a sign of how important the case was to him. US Supreme Court Chief Justice John Roberts Jr., Justice Elena Kagan, Justice Brett Kavanaugh and Justice Amy Coney Barrett are seen attending the State of the Union in 2026 President Donald Trump speaks to reporters at the White House Protesters are seen demonstrating against Trump's immigration policiesBut as he stared down the Justices in the face, including those he appointed himself, they expressed skepticism. The Supreme Court's longest-serving conservative, Clarence Thomas, did not hold his fire in a 92-page fiery dissent, and said of the ruling: 'I am not sure that today’s opinion will stand the test of time.' 'The Citizenship Clause ‘added greatly to the dignity and glory of American citizenship,'' Thomas said, adding: 'Today’s opinion devalues that citizenship. I respectfully dissent.' He was joined by another conservative on the bench, Justice Neil Gorsuch. case hinged on narrowly interpreting the 14th Amendment's Citizenship clause: 'All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens.' The President's legal team argued that the children were not 'subject to the jurisdiction' of the US when they were born. They claimed that 'subject to the jurisdiction' means full allegiance to the US, and parents unlawfully in the US do not qualify, and neither should their children.Senior Trump administration officials viewed the executive order as a key component of Trump's hard-line immigration agenda— an issue that has become a defining feature of his second White House term. Opponents had argued that a ruling in Trump's favor would have upended long-held notions of citizenship, and would yield immediate, operational consequences for infants born in the US, putting the impetus on Congress, and the administration, to immediately clarify the status of the newborns.After Trump signed the citizenship executive action in February 2025, the directive was immediately challenged by states and civil rights groups, including the ACLU. The order has never taken full effect. The case, Trump v Barbara, pitted Trump's order against a group of affected families nationwide, backed by the ACLU and other groups. These groups contend that the 14th Amendment guarantees citizenship to anyone born on US soil, and has been read that way for more than a century - and upheld in laws passed by Congress in the decades since.Many of the Justices seemed skeptical of the Trump administration's arguments during the April 1 oral arguments. Supreme Court justices pose for their group portrait in 2022In what proved to be a telling exchange, Chief Justice John Roberts told US Solicitor General John Sauer at the outset of oral arguments that he viewed a key argument from the Trump administration as 'quirky.'Roberts noted he was having a hard time making sense of the Trump administration's legal position on the 14th Amendment's exceptions to birthright citizenship, citing exceptions the administration listed, including children of ambassadors, children born on warships, and other very limited groups.'I'm not quite sure how you can get to that big group from such tiny and sort of idiosyncratic examples,' Roberts noted.'We're in a new world now,' Sauer told Roberts.'It's a new world,' Roberts said in response, 'but it's the same Constitution.'Trump's own nominees— Justices Amy Coney Barrett, Brett Kavanaugh, and Neil Gorsuch— also appeared skeptical of the administration's arguments in April.Justice Kavanaugh cited the passage of the 1952 Immigration and Nationality Act (INA), noting that it essentially mirrors the text of the 14th Amendment and text of the 1898 case. The President made history in April by becoming the first sitting president to attend Supreme Court oral arguments in person Trump speaks during an event in the Oval Office of the White House on June 22'One might have expected Congress to use a different phrase if it wanted to try to disagree with [precedent set in] on what the scope of birthright citizenship, or the scope of citizenship, should be,' Kavanaugh said.'I am not seeing the relevance as a legal constitutional interpretative matter,' Kavanaugh finally told Sauer, after a brief back-and-forth.