Trump immunity case live updates: Supreme Court hears historic arguments

Justice Clarence Thomas opened questioning by getting to the heart of the case: where is the “source” of presidential immunity and how would the court come to decide what acts fall under that scope.

First, he asked Trump’s attorney to be “more precise as to the source” of supposed presidential immunity.

John Sauer responded that it comes from the executive vesting clause of the Constitution.

Thomas then pressed how exactly the court would “determine what an official act is,” to which Sauer said acts fall within the “outer perimeter” of a president’s official duties.

Trump’s attorney, John Sauer, addressed the justices first, saying in his opening statement, “Every current president will face de facto blackmail and extortion by his political rivals while he is still in office.”

Sauer also called out controversial policies of other presidents, such as George W. Bush’s regarding the Iraq War and Barack Obama’s drone strike against a US citizen, while saying the implications of the court’s decision here “extend far beyond the facts of this case.”

Oral arguments have begun in Donald J. Trump v. United States.

Arguing for Trump is attorney D. John Sauer. Presenting for Smith is Michael R. Dreeben, who has argued more than 100 cases before the nation’s high court.

As Trump headed into court on Thursday morning for his ongoing trial in New York (he has pleaded not guilty), he continued to weigh in on the presidential immunity case.

“I think that the Supreme Court has a very important argument before it today,” he told reporters as he entered the hallway inside a Manhattan courtroom for his hush money trial. “I would have loved to have been there but this judge would not allow me to be there.”

Trump argued that the president “has to have immunity,” repeating a claim that federal prosecutors and some judges have so far said would uphold the rule of law.

“This has to do with a president in the future for 100 years from now,” he said. “If you don’t have immunity, you’re not going to do anything. You’re going to become a ceremonial president. It’s just going to be doing nothing, you’re not going to take any of the risks, both good and bad.”

-ABC News’ Kelsey Walsh and Michael Pappano