ALEXEI NAVALNY, Russia’s opposition leader, has become the biggest thorn in Vladimir Putin’s flesh. Last year Russian security forces tried and failed to kill him by poisoning him with a nerve agent. The authorities then arrested him in Moscow in January. On June 9th—just days ahead of Mr Putin’s summit with President Joe Biden—a court banned groups affiliated with Mr Navalny, ruling that they are “extremist organisations”. Why is Russia’s president so afraid of Mr Navalny?

For an answer, go back a decade. In 2011, when Vladimir Putin’s United Russia party won a rigged parliamentary election, Mr Navalny, then a popular blogger and fierce critic of the Kremlin, led tens of thousands of protesters to demand a “Russia without Putin”. They did not get their wish, but Mr Putin has tried (and so far failed) to get a Russia without Mr Navalny—and many of his supporters.

Mr Navalny is the first opposition politician since the collapse of the Soviet Union to mobilise a powerful opposition movement that draws together many strands of society, from working-class neighbourhoods in the regions to the urban intelligentsia in Moscow. He uses the web (still relatively free) to burst the state-television monopoly and to mobilise big street protests. He represents a generational shift, which has often been an engine of political change in Russia, and has exposed the main weakness of Mr Putin’s regime: its moral and financial corruption and its lack of vision for Russia’s future.

Though Mr Navalny has never been allowed to run for president—the Kremlin has barred him from standing and has banned his party—his activism and his fight against corruption have attracted millions of supporters. Mr Navalny has done this in part through canny use of social media (he has 2.6m followers on Twitter and 6.5m subscribers on YouTube), where he mocks the Kremlin and exposes its failings.

He has called on his supporters to vote for whoever is best placed to defeat the Kremlin’s candidate, no matter which party they represent, a tactic he calls “smart voting”. This approach contributed to the ruling party losing almost half of its Moscow city-council seats in local elections in 2019.

Last March Mr Putin scrapped term limits that would have forced him to stand down as president in 2024, but his ability to govern still depends on the ruling party retaining control. A parliamentary election is due in September; in an independent poll in March approval ratings for his party were just 27%. Trust in the president is slipping, too. With the economy stagnating and real disposable incomes falling for the past six years, appetite for protest has been rising.

Mr Putin’s sole preoccupation is his own survival. The Kremlin’s fear of Mr Navalny spearheading a mass protest movement, of the kind that broke out in neighbouring Belarus last year, has driven the Kremlin to more extreme action, such as the attempt to neutralise Mr Navalny by poisoning him with a nerve agent in August 2020. Mr Navalny survived the attack and was evacuated to Germany for treatment, where Mr Putin probably hoped he would stay and be forgotten. Instead, Mr Navalny identified his poisoners and returned to confront the Russian president. Officially he languishes in prison for breaking the terms of his probation (related to a previous trumped-up conviction for fraud) while recovering in Germany.

Now Russian security services have mobilised all their resources to crush Mr Navalny’s movement and to purge Russian politics of grass-roots opposition. They have outlawed Mr Navalny’s anti-corruption foundation, along with his regional network, in effect equating its members to terrorists and banning them from elections. A servile Russian court, which made its proceedings secret, rubber-stamped the decision. “When corruption [becomes] the foundation of the state, those who fight against it [become] extremists,” Mr Navalny wrote in an Instagram post, via his lawyers.

Yet, banning Mr Navalny’s organisation is unlikely to stop a historic shift that he has helped bring about. As he added on Instagram, "What difference does it make what we are called?...We are millions and we are not going anywhere”.