In 1976, a year after he was awarded the Nobel Peace Prize for being “spokesman for the conscience of mankind”, Andrei Sakharov was classified by the KGB as “domestic enemy number one”.

Alexei Navalny, the Russian opposition activist arrested on his return to Moscow on Sunday, may not possess the same righteousness as Sakharov, the most famous of Soviet dissidents. But there is no doubting his courage. Or that today’s Kremlin regards him as its greatest domestic enemy. As with the nuclear scientist half a century ago, Mr Navalny’s treatment by the Russian government has only elevated his status as a symbol of repression.

The cruel suppression of Sakharov came to symbolise the moral bankruptcy of the Soviet system and helped galvanise western, especially European, opinion against it. It would be naive to think Mr Navalny’s treatment will have a similar effect. The cold war is long over and most western capitals have other interests beyond countering Russian aggression.

But just as the KGB fretted about Sakharov’s impact, so Russian president Vladimir Putin fears that Mr Navalny can mobilise opinion against his increasingly autocratic regime. Russia is due to hold parliamentary elections in September and Mr Navalny and his fellow activists have been organising surprisingly successful campaigns in local elections. They are rallying support for any candidate able to beat incumbents from Mr Putin’s ruling party, which has suffered a fall in popularity ratings to record lows in recent months.

How else to explain the extraordinary, almost farcical measures the Russian authorities took to prevent Mr Navalny from enjoying a welcoming party of supporters on his return from Berlin, where he spent five months recovering from an assassination attempt blamed on the Kremlin. First, riot police tried to remove his supporters and journalists waiting in the terminal at Moscow’s Vnukovo airport. Then, minutes before his flight from the German capital was due to land, it was diverted. A snowplough had, conveniently, stalled on a runway.

“Navalny’s reception by the authorities at the airport is the best evidence of how afraid they are of him,” Andrei Kolesnikov of the Carnegie Moscow Center said on Twitter. “They themselves are inflating the importance of Navalny, turning him into academician Sakharov.”

Mr Navalny’s prominence was affirmed last year, when he was poisoned with a banned chemical weapon during a visit to Siberia. Last month he published an investigation which plausibly demonstrated that it was the FSB, Russia’s main security service, that carried out the murder attempt. He then humiliated the FSB by releasing a recording in which one of its operatives was duped into admitting responsibility.

Until last year’s poisoning the authorities had sought to contain him with harassment, repeated arrests, short detentions and disqualifications from office. Now they are likely to lock him up for a long time. Upon his arrival on Sunday, he was arrested for flouting the terms of a suspended sentence for fraud that he (and the European Court of Human Rights) says is trumped up. On Monday, Mr Navalny was sentenced to 30 days in jail after a summary hearing, for which he was given one minute’s notice. He could face another three years behind bars when the case returns to court. Other embezzlement charges are pending.

“For the authorities, how they viewed Navalny changed not as much after he was poisoned, but after the . . . FSB exposés. No longer is he a small-time crook, but an enemy who must be humiliated, crushed, punished,” says Tatiana Stanovaya of political consultancy R Politik.

This travesty of justice is a challenge to Mr Putin’s western critics, especially incoming US president Joe Biden who wants to rally allies in defence of democracy. His administration will need to persuade European capitals to move beyond ritual condemnation. The key will be German chancellor Angela Merkel. She has held the line on sanctions over Russia’s aggression in Ukraine, rebuffed French pressure to reset ties with Moscow and strongly condemned the assassination attempt against Mr Navalny. She should now follow through with further economic sanctions as part of an EU wide package, including a moratorium on the new Nord Stream 2 pipeline bringing Russian gas to Germany. The Navalny case will also be a test for Armin Laschet, the new head of Ms Merkel’s party, the Christian Democrat Union, who has been rather soft on Moscow.

The Kremlin’s high-visibility persecution risks turning Mr Navalny into a rallying point for domestic opposition. He must be effective if Mr Putin fears him so much. The Russian leader does not seem to care that dispensing with due process makes Mr Navalny a symbol of the abuses of an authoritarian regime. But the west must.