It's the biggest judicial defeat that US President Donald Trump has suffered in his second term – a ruling that strikes at the heart of the sweeping tariff regime he has cast as the centrepiece of his economic policy. And the key player who fought Trump to the death is Indian-American lawyer Neal Katyal, who is regarded as the greatest courtroom star of his generation.

Trump is not the first US President whose policies Katyal has fought and won against. Almost 20 years ago, Katyal had argued in the US Supreme Court on behalf of Salim Ahmed Hamdan, a Yemeni man who had been a chauffeur for Osama bin Laden. In that trial, Katyal had challenged and defeated George W. Bush’s policy of military trials at Guantanamo Bay

Trump’s reaction was fast and furious on hearing the news of his lost court case and the collapse of the great tariff wall that he has erected – a web of import duties he argued would help rebuild US manufacturing and rebalance trade.

He immediately held a combative press conference, calling the ruling “ridiculous”, denouncing the judges who ruled against his tariff actions as a “disgrace” and branding the group of small-business owners who brought the suit before the Supreme Court “sleazebags”.

The US President declared that he had tried not to make comments before the judgment came out. “I wanted to be well-behaved because I didn't want to do anything that would upset the decision of the court,” he said, adding, “Because I understand the court. I understand how they are very easily swayed. I want to be a good boy.”

But this time the spotlight shifted away from Trump and on to the bespectacled 55-year old Katyal, who fought the case for the business proprietors, many of whom said the tariffs were crippling them with higher costs.

When the ruling was handed down, Katyal posted a one-word triumphant tweet: “Victory.” Later, when facing the cameras, he spoke about the rule of law, and dismissed what he said was the US President’s outrageous behaviour.

“The President can’t do this ridiculous ‘I’m the President [routine]. I can do whatever I want.’ Today, the Supreme Court stood up for the rule of law. Stood up for Americans everywhere. Presidents are powerful, but our Constitution is more powerful still,” Katyal said.

At the core of the ruling was a basic principle of the US Constitution: “Only Congress can impose taxes on the American people and that’s what tariffs are. Tariffs are taxes,” Katyal stressed. One commentator reckoned that the Supreme Court ruling could be summed up in those three words: tariffs are taxes.

Katyal is no stranger to the justices of the Supreme Court. He has argued 54 cases before the court, a remarkable tally given that America’s highest court hears only a limited number of cases each year. Over the course of his career, he has handled cases spanning civil rights, federalism, separation of powers and national security. He has scored major wins before, but this ranks as his most politically significant.

“The Supreme Court hasn’t struck down such an important policy initiative in about 90 years, since 1935 when they struck down FDR’s first New Deal,” Harvard Law School professor Noah Feldman told Bloomberg.

Feldman also noted that this is the first time the Supreme Court has stood up to Trump. Former US President Franklin D. Roosevelt, known as FDR, introduced the New Deal, which was a sweeping programme of economic relief measures to combat the Great Depression.

Katyal’s resume is formidable. As the acting solicitor general during the Obama administration, he successfully defended the Affordable Care Act, the healthcare reform known as Obamacare, and also the Voting Rights‘ Act. It was also during his time that the US Department of Justice offered a full apology to ethnic Japanese and others who had been interned during World War II, a landmark reckoning. Besides that, he also took on cases arguing against the holding of prisoners at Guantanamo Bay. Like Hamdan.

From the start, Katyal seemed destined for great things. He studied at Dartmouth College and then Yale Law School. Afterwards, he went on to clerk for US Supreme Court judge Stephen Breyer. Along the way, he also did a project for President Bill Clinton on the need for expansion of pro bono legal work. He returned to teach at Georgetown University Law Center and became a partner in a law firm. He’s currently with a leading law firm Milbank.

Katyal’s parents are both professionals. His father’s an engineer and his mother is a paediatrician, He effusively praises the American way of life, where the son of immigrants has been able to rise to the level that he has been able to.

Speaking to reporters he framed his legal win in personal terms. “I was able to go to court, the son of immigrants, and say on behalf of American small businesses, ‘Hey, this President is acting illegally'."

It was, he said, proof of something “extraordinary” about the American system, “the idea that we have a system that self-corrects… you might be the most powerful man in the world, but you still can’t break the Constitution.”

His opposition to Trump has been clear for a long time. In 2019, he co-authored with Sam Koppelman a book titled Impeach: The Case Against Donald Trump, laying out a legal precedent for removing the President from office.

What’s next for Katyal? When he became acting solicitor general under Obama, he replaced Elena Kagan, who became a Supreme Court judge. In a future Democratic administration, he would surely be a top candidate on the shortlist for the country’s highest bench.