Éric Zemmour, a far-right pundit, tried to revive his flagging campaign Sunday in a place that is familiar to hopefuls of his ilk.PARIS — With its immense forecourt opening onto a breathtaking view of the Eiffel Tower, the Trocadéro Plaza in Paris offers an ideal setting to revive a flagging campaign for the French presidency. Twice in the past decade, tens of thousands of people have flocked there, responding to calls from embattled right-wing contenders looking for support.A third attempt came on Sunday, when Éric Zemmour, the far-right pundit turned presidential candidate, held a massive rally at the Trocadéro designed to halt his slide in the polls, exactly two weeks before the first round of voting.“I will fight to reconquer our identity, I will fight to regain our prosperity,” Mr. Zemmour told tens of thousands of supporters who waved a sea of French flags under a blazing sun.Sunday’s rally, one of the biggest of this year’s elections, had all the trappings of a last-ditch attempt to revitalize a campaign that started with a bang and then gradually stalled, as Mr. Zemmour, 63, got bogged down in controversies and struggled to broaden his voter base.He entered the presidential race last fall, putting his prolific career as a polarizing far-right writer and television star behind him and promising to shake up French politics with his hard-line views on immigration, Islam’s place in France and national identity.Many people at Sunday’s rally were drawn by support for Mr. Zemmour’s conservative positions on immigration. The placard reads, “So that France remains France.”Julien De Rosa/Agence France-Presse — Getty ImagesAnd shake it up he did. For months, through his active presence on social and news media as well as his frenzied rallies, he shaped the public debate by pushing it further to the right. He popularized the concept of the “great replacement” — a racist conspiracy theory stating that white Christian populations are being replaced by nonwhite immigrants — rewrote some of the worst episodes from France’s past and promoted divisive ideas such as a proposal to force parents to give their children “traditional” French names.His meteoric rise in the polls — he briefly ranked second in mid-February — turned him into an unexpected runoff contender and a serious threat for Marine Le Pen, the longtime leader of the far right, and Valérie Pécresse, the candidate of the mainstream right.But his ratings have gradually slipped for a month, putting him in fourth or fifth place, after the war in Ukraine exposed two of his biggest flaws: his past sympathy for President Vladimir V. Putin of Russia and his neglect of the issue of economic inequalities.In a 2018 interview, Mr. Zemmour said he “would dream” of a French equivalent of Mr. Putin, praising his attempt to restore the grandeur of “an empire in decline” — words that have haunted him since Russia invaded Ukraine, severely denting his credibility on international affairs. The candidate also provoked an outcry after he first opposed welcoming Ukrainian war refugees, saying it would further “destabilize France, which is already overwhelmed — I do say overwhelmed — by immigration.” Ukrainian evacuees crossing the border into Palanca, Moldova, this month. Mr. Zemmour provoked an outcry after at first opposing an influx of Ukrainian refugees.Mauricio Lima for The New York TimesBut it is his failure to respond to the economic hardship created by the war that has most affected his standing. Mr. Zemmour has long defended liberal positions on the economy, which have done little to allay voters’ fears about rising energy prices. By contrast, his competitors, Ms. Le Pen and Jean-Luc Mélenchon, a far-left candidate, have benefited from this concern, having long campaigned against economic inequality.“He has focused so much on identity, immigration and security,” said Bruno Cautrès, a political scientist at the Center for Political Research at Sciences Po university in Paris, “that it has prevented him from embodying anything else in the eyes of the voters.”In the fall, Mr. Zemmour had pinned his hopes on his ability to appeal to “the patriotic bourgeoisie and the working classes.” But attendance at Sunday’s rally suggested that he mainly attracted bourgeois voters.“Sovereignty, grandeur, identity — this guy thinks exactly like me,” said Benoît Bergeron, a 68-year-old Zemmour supporter wearing a tweed jacket, who had crossed the Seine from his upscale Left Bank neighborhood to join the rally.Mr. Bergeron said the last time he had joined a demonstration was to support La Manif Pour Tous, a large movement opposing same-sex marriage that upended France in 2013. Several supporters in the crowd said Mr. Zemmour was the best representative of a conservative generation that emerged after that movement.Mr. Cautrès said Mr. Zemmour had a limited voter base and scored well mainly among segments of the upper middle class, the elderly and conservative Catholics. “It’s not something that propels you to the second round of the presidential election,” he said.Against a backdrop of sinking poll numbers, Mr. Zemmour has tried to refocus the debate around immigration by toughening his already polarizing stance. Warning that France will become “a Muslim country” by 2060 if current migration levels persist, he promised last week to create a “Ministry of Remigration” and deport 100,000 “undesirable foreigners” each year, if elected.Marine Le Pen, the longtime leader of the far right, is now polling at 20 percent in voting intentions, about twice the level of Mr. Zemmour.Johanna Geron/ReutersBut the proposal only caused further controversy and accentuated his image as an extreme politician. “He didn’t run a campaign to bring people together, but he ran one that was more divisive, more provocative every day,” said Robert Ménard, a French radical right-wing mayor and longtime acquaintance of Mr. Zemmour who supports Ms. Le Pen.At the rally, Mr. Zemmour’s speech was filled with populist overtones, with attacks against the news media and the elites, who he said where trying to undermine his candidacy. “Nothing and no one will steal this election from us,” he told the roaring crowd.The candidate’s radical messaging has also had the unexpected effect of sanitizing the image of his direct far-right competitor, Ms. Le Pen, a goal she has long been pursuing. Ms. Le Pen is now polling at 20 percent in voting intentions, about twice the rate for Mr. Zemmour, and appears on track to reach a runoff with the incumbent, President Emmanuel Macron.“He has normalized Marine Le Pen,” Mr. Ménard said.Perhaps the biggest impact of Mr. Zemmour’s campaign will be its lasting effect on French politics, which have increasingly lurched to the right. Polls show that two-thirds of French people today are worried about the “great replacement.” Depending on his performance in the first round of voting, Mr. Zemmour may also force a complete reshuffle of the French right. Several leaders of Ms. Le Pen’s and Ms. Pécresse’s parties have already joined his campaign.Several supporters at the Trocadéro on Sunday said they did not trust the polls. “We’re at a turning point,” said Stéphanie Vitry, a company manager, who was convinced Mr. Zemmour would come out ahead in two weeks. Otherwise, she said, “it’s the end of France.”But some did not hide that they had largely given up hope that the far-right candidate would reach a second round.“I confess that I’m not very optimistic,” said Oxana Herbeth, 23, a former Le Pen voter who had turned to Mr. Zemmour, attracted by his tough line on immigration and security.It did not help that the Trocadéro has also been symbolically associated with the downfall of the French right. The past two presidential candidates of the center-right party Les Républicains held big rallies there — before being defeated on Election Day.“To gather the right at the very place where it has failed,” Mr. Ménard said. “Strange idea.” More