FEATURE|The 39-year-old French-American Berkeley professor is campaigning to have voters approve, in a November 3 referendum, a measure that would temporarily impose a 5% tax on the wealth of billionaires living in the state. Some of his colleagues consider that his activism has begun to overshadow his scientific approach.
In the darkness of the Airbus 350, high above the Atlantic, almost every screen played romantic comedies or cartoons. Only one screen remained stubbornly switched off for the entire 11-hour flight: that of Gabriel Zucman, who was fine-tuning a "manifesto against the international oligarchy" on his laptop.
On Saturday, September 26, the French-American economist got up at 4 am in Budapest, where he had gone to help the new Hungarian government with a project for a wealth tax. He ran to avoid missing his connection in Paris. Upon landing in San Francisco, he was as fresh as a daisy. "I'm fired up! I can't wait to dive into the fight." We followed him for five days. Unaffected by jet lag, he went from conference to meeting, to interview, to filming messages that he planned to "bombard" social media with, helped by three comms people who fluttered around him.
The fight centers on Proposition 40, which Californians are set to vote on during the November 3 midterm elections. Voters must answer yes or no to a one-time 5% tax on total wealth – both professional and personal – of the roughly 250 Californian billionaires.
The money raised, estimated at $100 billion, is intended to save the health coverage of 3.5 million Californians, threatened by cuts imposed by the One Big Beautiful Bill, signed on July 4, 2025, by President Donald Trump. Backed by the SEIU-UHW (Service Employees International Union-United Healthcare Workers West) union – which collected the 875,000 signatures required to put it to referendum – Proposition 40 draws directly on the work of two French-American professors at the prestigious University of California, Berkeley: Zucman, 39, and Emmanuel Saez, 53, his mentor and friend.
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The economists spent nearly 10 years working on the explosion of wealth inequality, which they describe as "the most significant social and political event of the early 21st century," as well as on the tax rates of the ultra-wealthy, which various tax loopholes and legal arrangements have kept extremely low. In 2023, Zucman joined the Paris School of Economics and sparked a heated debate in France over the so-called "Zucman tax" (2% of net wealth above €100 million), which led to him being labeled a "pseudo-academic" and a "far-left activist" by Europe's richest man, Bernard Arnault.
But his campaign is international, it includes Sweden, Germany, Belgium, England and Spain. In 2024, he even traveled to São Paulo, Brazil, to present his ideas to the finance ministers of the G20, which was then chaired by President Lula.
Two competing referendums
"Look, my billionaires are right there!" Zucman pointed to the window. His office at Berkeley is next to Saez's, on the sixth floor of the ugliest building on campus, a brutalist concrete block called Evans Hall. At the foot of the building, a few parking spots are marked with signs reading "Reserved for Nobel Prize Winners." Zucman and Saez each received, in 2023 and 2009 respectively, the highly prestigious John Bates Clark Medal, which in economics often precedes a Nobel. Hardly what you would call "pseudo-academics."
"On the right, there's Mount Tamalpais, the Golden Gate and over there, in the mist, the San Francisco skyline. The people trying to kill Proposition 40 live over there!" Several major business leaders, claiming that this tax could derail California's economy, have spent outrageous amounts of money to make sure it fails. The figures, which are available online, are mind-boggling.
On that day, they had already spent $220 million, flooding television with openly false commercials ("Everyone will be taxed," claimed a Hispanic woman, for example) and bombarding phones with similar text messages. They also set up two rival referendums restricting the use of taxation, Propositions 41 and 42. If either one receives more votes than "Prop 40," it will kill it. Google co-founder Sergey Brin has led the effort. He personally put $100 million on the table. "At the rate they're going," predicted Zucman, "they should spend a total of $400 million before November 3. That's unprecedented. They're scared, and they're right to be!"
The fight is unequal, but that does not discourage him. When he launches, like a rocket, into his activist enthusiasm, his cheeks flush and no objection can stop him. According to him, whether it succeeds, the battle over Proposition 40 could change the face of the world – nothing less. "If it passes, people will realize that we can raise $100 billion without triggering an economic collapse, and that will launch a global movement. Other US states, other countries will follow. Don't forget that the conservative tax revolution that swept the world in the 1980s started here, in 1978, with Proposition 13, which limited the possibility of tax increases."
And if the "yes" vote does not win? "Then this episode will have exposed to the whole world the many tactics used by the ultra-wealthy to protect their money and their power." According to Zucman, that would be a first step.
The next day, he's meeting the leader of the camp supporting Proposition 40, Dave Regan, at the headquarters of SEIU-UHW, in the neighboring city of Oakland. The union boss is a burly 60-year-old man, wearing a plaid shirt with his sleeves rolled up. His office is gray, as are the armchairs. The two men discussed the maneuvers of Gavin Newsom, the Democratic governor of California (and a likely candidate for the 2028 presidential election), who is opposed to Proposition 40.
They assessed the state of affairs. The coffers were empty: "We spent $25 million just to collect signatures. There's nothing left for TV spots. We're making do with social media." The polls still show the "yes" side in the lead, but the billionaires' advertising campaign is starting to have an effect: The margin is shrinking. "True, but it hasn't flipped," Regan reassured himself. He thanked his visitor from France for persuading six Nobel laureates to join the cause. He did not rule out defeat, but, whatever happens, members of the organization will remain proud to have launched "a movement that will not stop."
A meeting with centimillionaire Saikat Chakrabarti, co-founder of the Justice Democrats organization which launched the career of politician Alexandria Ocasio-Cortez, a conference alongside Saez and Robert Reich, US secretary of labor under Bill Clinton who has become something of a guru for the left: Zucman pressed on with his tour, tireless. "He has the determination of a top-level athlete," his wife had warned, labor economist Claire Montialoux, with whom he has three children.
Zucman did not inherit his activism. He was born into a well-to-do Parisian family. Many of his relatives were doctors, some were antique dealers and on his mother's side, there were timber industry entrepreneurs. One particularly influential grandmother was Dr. Elisabeth Zucman (1930-2019), a communist who raised national awareness in France about the issue of multiple disabilities. "A left-wing family, but not an activist one," summed up his brother Guillaume, who worked in several ministers' offices under President Emmanuel Macron, to the skeptical gaze of his older brother.
As a high school student, Gabriel was not particularly interested in politics. Hardworking and curious about everything, he followed a path of academic excellence: preparatory classes at prestigious institutions including Paris's Henri-IV high school and then the Ecole Normale Supérieure. There, he met economist Thomas Piketty, an expert on inequality. "He came to see me, very determined, very mature, to ask if I would supervise his master's," recalled the author of Capital in the Twenty-First Century. "I put him to work on the statistics of the ISF [France's wealth tax], an area where there had been very little research at the time."
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Zucman was still searching for his path at the time. He did a six-month internship at the brokerage firm Exane, then another at the Finance Ministry. He tried to understand the financial crisis that shook the world in 2008. Piketty persuaded him to return to academia. The student embarked on a doctoral thesis under Piketty's supervision, focusing on fortunes hidden in tax havens. He immersed himself in international financial data. "He fell into it and never came out," Piketty joked.
In their offices in the 14th arrondissement's Boulevard Jourdan, where the Paris School of Economics is located, the economist and his doctoral student spent months poring over public and private wealth data from several countries, going back to the early 18th century. "We divided up the countries. It was an enormous task. Between 2010 and 2012, we were together all the time," Piketty recalled with nostalgia. Their article, "Capital is Back: Wealth-Income Ratios in Rich Countries 1700–2010," showed that wealthy countries were returning to levels of wealth accumulation similar to those seen at the end of the 19th century. The U-shaped curve caused a sensation.
Then Zucman crossed the Atlantic, drawn by the research of Saez, a close associate of Piketty. The two became very close, delving together into wealth inequality in the US. They meticulously quantified its spectacular rise, revealing to the world a phenomenon that had previously gone largely unnoticed.
"It was through our work that our radicalism on the subject emerged," they said in unison. Both researchers enjoy getting their hands dirty with data. Each built their reputation through work on data and the development of methodologies to process them. "Emmanuel works like a monk, 10 hours a day, seven days a week," Zucman said of Saez. "Gabriel has worked like an ascetic for 15 years," Zucman's wife said.
In academic articles, the two men documented the surge in wealth inequality in the US and highlighted for the first time that, at the top of the social ladder, the overall tax rate was lower than that paid by working and middle-class Americans. In 2019, they co-authored The Triumph of Injustice, a best-selling book offering solutions. At that time, they took their first step into the US political arena, providing their ideas to two of the candidates in the 2020 Democratic primaries, Bernie Sanders and Elizabeth Warren.
Although they share the same passion for painstaking scholarly work, Saez could not be more different from Zucman. He was born to a father from northeastern Spain, an executive at the telecommunications company Telefónica, and a mother who taught Spanish. They settled in the French Basque Country. In a pink surfer's T-shirt, he is tall, and his arms, which move expressively as he speaks, seem even longer. He smiles kindly and looks at you intently. Within the university, he is also held in high esteem, even by economists who completely disagree with him.
This is the case for Enrico Moretti, who has an office in the same corridor. He considers Proposition 40 "dangerous," saying it could "drive away some major entrepreneurs, reduce California's appeal and ultimately weaken tax revenues." That does not stop him from calling Saez "one of the giants of Berkeley." A somewhat reserved giant. "He is a kind and gentle man, who found in Berkeley an extension of the Basque coast where he grew up," mathematician Cédric Villani, who was his friend at the Ecole Normale Supérieure, told us. While Zucman does not shy away from the spotlight, Saez prefers to stay in the background. "Unfortunately, these days, the media approach me to defend this tax," he regretted. He does so "out of duty," because he believes in it.
On September 30, Zucman crossed the bay without his colleague to defend the billionaire tax at Stanford University. With its majestic Mission Revival-style buildings and tall trees, the campus looks very different from Berkeley's. There, you can see empty robot taxis and ultra-light bicycles. The air smells of eucalyptus and opulence. The university lies at the heart of Silicon Valley, the tech ecosystem. It houses the Hoover Institution, where libertarian economists are leading the fight against Zucman and Saez's ideas. According to them, Prop 40 would create an exodus of entrepreneurs and, ultimately, result in lost revenue for the state budget.
The roughly 150 students attending the lecture, eating pizzas provided for the occasion, did not go easy on the speaker, listing objections to taxing high-net-worth individuals. Zucman fielded their questions with casual ease. To make his point, he gave concrete, striking examples: "Jeff Bezos or Elon Musk declared, in some years, almost no income and therefore paid almost no tax. In fact, one year, Bezos paid so little that he qualified for a child tax credit!" He also delivered a few punchlines: "If someone who doesn't pay any taxes moves to Nevada, who really cares, right?"
At the end, several students of different nationalities came up onto the stage in the lecture hall. When the economist described the Hoover Institution's apocalyptic forecasts as "nonsense," one of them, who was affiliated with the center, became agitated: "You have no grounds to dismiss the possibility that major taxpayers will leave! What about the dynamics dictated by rational expectations [a libertarian theory according to which economic actors adjust their behavior to economic policies by anticipating their impact]? There are Nobel laureates who have demonstrated this."
Weary of the debate, the economist deployed his friendly face and his data as shields: "These threats of exodus are common, but, in reality, they never happen." The researcher remained courteous, but on substance, he did not budge one inch. This doesn't always sit well with his colleagues, who used to enjoy debating with him. "He has gone from a historical and quantitative analysis of inequalities to an activist approach. And he is now trapped by the public persona he has become. That makes scientific debate more difficult," said Antoine Levy, another French economist at Berkeley, who is strongly opposed to his colleague's ideas but still maintains a good relationship with him.
It is extremely rare for a top-level economist to cross over in this way and become an activist. But it would be a mistake to imagine Zucman as a lone wolf. He is less a Don Quixote than a Robin Hood, relying on a band of allies – a "tax force." These include Saez and Piketty, of course, but also Camille Landais and Nobel laureates Paul Krugman, Joseph Stiglitz and Esther Duflo. And, above all, the researchers at the International Tax Observatory, which he founded just before his return to France and is funded by European grants.
Based at the Paris School of Economics, the observatory already has 40 staff members, including 30 researchers. Zucman insisted that it include a public policy team to monitor developments and promote the researchers' proposals in the media and political debates in different countries. This was an innovation in the academic world. "I have to admit that at first I felt like I was inventing my own job," recalled Quentin Parrinello, the head of this team, who came from Oxfam France, where he was in charge of advocacy for "tax justice and inequalities."
Finally, to strengthen his strategy and communication, Zucman brought on board a man who has become essential to his operation: Pierre Natnaël Bussière, 32. This behind-the-scenes adviser, always on the move, accelerated the economist's transformation by making his messages go viral on social media, Instagram in particular. His career path has been truly unusual.
Born in Ethiopia to military parents, he was adopted as a child by a couple living in the Puy-de-Dôme region of central France. After studying law, this admirer of the philosopher Claude Lefort began a doctoral thesis in political theory, "The Wild Public Sphere: Democracy in the Digital Age," at the School for Advanced Studies in the Social Sciences, while also launching a strategy and communications consulting firm with his partner. He co-founded the left-wing political party Place Publique in 2018 with current presidential candidate Raphaël Glucksmann. Bussière became the driving force behind Place Publique's 2024 European election campaign, the success of which owes much to him. He later distanced himself when he realized that "Glucks" was shifting toward the political center.
A summit against oligarchy in November
Bussière challenged Glucksmann. Now, he's pushing Zucman. His obsession: making the economist's messages more effective. When the term "Zucman tax" appears in the press, he gleefully plays it up ("I would have preferred the Arnault tax," Zucman grumbled). Bussière also came up with the provocative title for the economist's latest work: Les milliardaires ne payent pas d’impôt sur le revenu et nous allons y mettre fin ("Billionaires Don't Pay Income Tax, and We Are Going to Put an End to That," 2025).
On a marble bench at the foot of the chiming campanile on the Berkeley campus, he recalled: "We decided to publish this book over drinks, after a debate organized in September 2025 with Philippe Aghion [Nobel Prize-winning economist, who is very opposed to the tax, but has great respect for his young colleague]. I suggested the title, then Gabriel wrote this little book in just a few days." The two men share a love for intellectual sparring in a Blitzkrieg style. According to his friend and fellow high school and École Normale Supérieure student Alexandra Roulet, a former adviser to Macron at the Elysée, "By letting his communications team coach him, Gabriel simplifies his message, which makes it divisive. At the risk of being counterproductive, because it reduces the chances of reaching a cross-party agreement on these issues of tax optimization."
The next step for Zucman and his associates is organizing the Summit Against the International Oligarchy, scheduled for November 21 at the Théâtre de la Concorde in Paris. The economist has invited many prominent figures, including Senator Sanders, several ministers and a collection of Nobel laureates. The conference is set to conclude with the signing of a manifesto advancing three proposals to rein in the power of billionaires: a wealth tax, of course, a mechanism to limit shareholder interference in the media and an international public fund to oversee the capital of artificial intelligence companies.
Bussière has already crafted his narrative: "The Lippmann Colloquium [Walter Lippmann was an American intellectual who died in 1974], held in 1938 in Paris, marked the beginning of neoliberalism, which ended up dominating the world from the 1980s onward. Who knows, maybe we can spark the same thing with the November 21 summit, to bring about a different, more humane model."
Before catching his flight home, Zucman once again let himself be filmed by Bussière and his team. They set up their camera on San Francisco's Billionaires' Row, a stretch of three city blocks − or rather, three blocks of extravagant mansions located in the heart of the upscale Pacific Heights neighborhood, with sweeping views of the bay, the Golden Gate Bridge and Alcatraz Island. Laurene Powell Jobs, the widow of Steve Jobs (Apple), Larry Ellison (Oracle), Jeremy Stoppelman (Yelp) and many other ultra-wealthy individuals live there. Backing up the analyses by Zucman and Saez on the explosion of wealth, this small neighborhood was still called Millionaire's Row just about 15 years
