President Trump arrived at the Supreme Court on Wednesday for oral arguments over his executive order to restrict birthright citizenship, the first time a sitting president has attended a high court argument, according to legal scholars.Why it matters: Trump's unprecedented appearance underscores how much the president's second-term agenda depends on a Supreme Court that has handed him both major wins and stinging defeats.State of play: Trump told reporters he was "going" to the hearing "because I have listened to this argument for so long."The president previously said he might attend last year's Supreme Court tariffs argument, but he ultimately stayed away. The court struck down his tariffs, and he called the justices who ruled against him unpatriotic.The president's motorcade arrived at the court around 9:50am ET, according to multiple media reports. Context: Trump on his first day back in office signed the order to restrict a right rooted in the U.S. Constitution that the Supreme Court affirmed more than 125 years ago.Between the lines: The president acted on a once-fringe belief that U.S.-born children of undocumented immigrants have no right to U.S. citizenship and are part of a conspiracy theory that's rooted in racism to replace white Americans, per Axios' Russell Contreras.He posted on Truth Social this week that birthright citizenship "is about the BABIES OF SLAVES" and was never meant for immigrants."Dumb Judges and Justices will not a great Country make!" he wrote on Monday.Courts have held since 1898 that the amendment applies to virtually all children born on U.S. soil.Zoom out: Trump railed against Supreme Court justices who struck down his sweeping tariffs agenda in a majority ruling in February.However, the high court sided with him in several cases last year, including letting him fire federal workers, resume mass deportations and ban transgender people from military service.What they're saying: The American Civil Liberties Union, which is challenging the executive order, called the case "one of the most important … in the last hundred years" in a statement. "If President Trump wishes to comes to the Supreme Court to watch the ACLU school him in the meaning of the Constitution and birthright citizenship, we will be glad to sit alongside of him in that very court," said ACLU Executive Director Anthony D. Romero in a statement.Go deeper: The Supreme Court cases that could shape 2026