Trump was driven by motorcade from the White House and arrived before the arguments, wearing a red tie and dark suit.
He was seated in the first row of the public section of seating in the ornate courtroom.
Trump and other attendees rose to their feet as the court marshal made the customary announcement beginning with “Oyez! Oyez! Oyez!” – meaning “Hear ye!” – to mark the beginning of the court session.
Chief Justice John Roberts did not acknowledge Trump’s presence before announcing the beginning of arguments in the case known as Trump v Barbara.
Outside the neoclassical courthouse on Capitol Hill, demonstrators gathered ahead of the arguments, some holding anti-Trump signs including ones reading “Trump must go now.”
Above Trump in the courtroom were friezes featuring symbols and personages of law and order, from the biblical figure Moses bearing the Ten Commandments to the Chinese philosopher Confucius through former Chief Justice John Marshall whose opinion in a landmark decision established the Supreme Court’s power of judicial review.
Trump faced forward toward the bench where the nine justices were seated as applicants to the Supreme Court bar were identified by name, raised their right hand and swore an oath stating that “as an attorney and as a counselor of this Court, I will conduct myself uprightly and according to law, and that I will support the Constitution of the United States”.
There appeared to be more security personnel than usual in the courtroom.
The Supreme Court has backed Trump in a series of rulings issued on an emergency basis since he returned to the presidency last year.
Those decisions came on matters including immigration, mass federal layoffs, cutting foreign aid, dismantling the education department, banning transgender people from the military and other areas.
However, the court on Feb 20 ruled against Trump in a major case testing the legality of the sweeping global tariffs he imposed last year under a law meant for use in national emergencies.
Since the tariffs ruling, Trump has lashed out repeatedly at the Supreme Court and the six justices who ruled against him in that case.
Trump is the first sitting president to attend an oral argument at the Supreme Court, according to Clare Cushman, the resident historian at the Supreme Court Historical Society.
There are examples of 19th century presidents arguing cases before the court – though not while in office – including John Quincy Adams, Grover Cleveland and Benjamin Harrison.
William Howard Taft, who served as president from 1909 to 1913, later became the chief justice on the Supreme Court.
Trump’s motorcade drove from the White House along Constitution Avenue and then Independence Avenue, passing the Washington Monument and the National Mall, with crowds watching from the sidewalk.
The Supreme Court’s 6-3 conservative majority includes three justices appointed by Trump during his first term in office – Neil Gorsuch in 2017, Brett Kavanaugh in 2018 and Amy Coney Barrett in 2020.
Barrett’s appointment gave the court its current conservative super-majority and ushered in an epoch in which the court has moved American law dramatically to the right including rulings rolling back abortion rights, rejecting race-conscious collegiate admissions policies, limiting the power of U.S. regulatory agencies and more.
Trump and senior officials in his administration often have denounced judges who have issued rulings against his policies, sometimes in highly personal terms.
‘They sicken me’
Three of the court’s six conservative justices – Chief Justice John Roberts as well as Gorsuch and Barrett – joined with the court’s three liberal members in ruling that Trump had overstepped his authority in imposing tariffs.
Trump was incensed at Gorsuch and Barrett in particular, calling them on the day of that ruling “an embarrassment to their families”.
Last week, Trump kept up his condemnation of his two appointees, saying that “they sicken me because they’re bad for our country”.
Trump after the tariffs ruling said he was “ashamed” of the three conservative justices who ruled against him, calling them “fools and lapdogs for the RINOs and the radical-left Democrats”.
RINO, meaning “Republican in name only,” is a term sometimes used by conservative Republicans to insult fellow Republicans viewed as disloyal to the party.
Trump after the ruling also claimed that the court “has been swayed by foreign interests,” but declined to provide any evidence.
A lower court blocked Trump’s executive order directing US agencies not to recognise the citizenship of children born in the US if neither parent is an American citizen or legal permanent resident, also called a “green card” holder.
Trump’s administration has said that granting citizenship to virtually anyone born on US soil has created incentives for illegal immigration and led to “birth tourism,” by which foreigners travel to the US to give birth and secure citizenship for their children.
Trump wrote on social media last year: “Birthright Citizenship was not meant for people taking vacations to become permanent Citizens of the US, and bringing their families with them, all the time laughing at the ‘SUCKERS’ that we are!”
Trump added: “But the drug cartels love it! We are, for the sake of being politically correct, a STUPID Country but, in actuality, this is the exact opposite of being politically correct, and it is yet another point that leads to the dysfunction of America”.