Alexei Navalny has picked up where he left off. The Russian opposition politician, released on Monday after 15 days in jail for his role in last month's large anti-government marches, hopes the momentum from those protests can boost his chances of taking on Vladimir Putin in next year's presidential election.

Inside the Kremlin, though, there is a different view of how likely Mr Navalny is to rouse a usually apathetic electorate — and of the real challenge to Mr Putin's authority. "The threat is not from Navalny, but from within," says one person who knows the president well.

More than 17 years after Mr Putin became president, the authoritarian system he built is showing signs of internal corrosion. Mr Navalny's ambitions are not expected to undo Mr Putin's re-election bid. But the uncertainty over what comes next is stirring ambitions and sparking jostling among power brokers in the Kremlin and across Russia.

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Mr Putin remains the supreme arbiter of Russia's politics. Co-opting elites from the security services to business, and across the political spectrum from nationalists to social democrats, the still popular leader — his support ratings remain above 80 per cent — has barred the rise of any challenger.

But Mr Putin would be 71 at the end of another six-year term — and there is no succession plan.

"It is stable because we all know he will run for another term and he will of course win," says a former senior official with close links in the administration. "But it is unstable because everything hinges on him."

The person who knows Mr Putin well says either a successor should be groomed or the president should "do a Yeltsin" — that is, try out potential successors as prime ministers, as Mr Putin's predecessor, Boris Yeltsin, did with him in 1999.

Dmitry Medvedev, the incumbent prime minister, has been a reliable associate of Mr Putin for years and is believed to have the president's promise that he can serve until 2018. But his position looks vulnerable. When Mr Navalny rallied participants to the March protests, he did so with a video accusing Mr Medvedev of amassing a corrupt property empire.

The prime minister has denied the accusations but the focus on him "makes it much more likely that Medvedev will have to go", says Tatyana Stanovaya, a political analyst at the Center for Political Technologies, a Moscow think-tank.

Sergei Kirienko, Mr Putin's chief of staff appointed last year, or Maxim Oreshkin, the youthful economy minister whose predecessor was detained for alleged corruption in November, are sometimes touted as successors to Mr Medvedev.

But Mr Putin is casting the net widely. Over the past two years he has sidelined dozens of Kremlin aides, cabinet members, security officials and regional leaders. Political heavyweights have been replaced by young men owing him their careers. "Those who prove loyal and efficient may enter the short list for future successors," says the former senior official. "This is a long-term vetting process."

One consequence has been a rise in infighting within the regime, with some of the political elite pushing their interests more forcefully.

As the weak oil price and Russia's recession have reduced budget revenues, regional governments are becoming less docile. The governors of economically successful Tatarstan and Kaluga criticised the federal government in January for redistributing too much money to poorer regions.

One extreme example of the frictions affecting those close to Mr Putin is in Chechnya, the North Caucasus republic. There, talks over the sale of Rosneft's local business to the regional government have pitted Igor Sechin, the pugnacious chief executive of the state oil group, against Ramzan Kadyrov, the region's belligerent leader.

Mr Kadyrov has refused to pay what Rosneft says its business is worth. "He is a pretty scary guy, but then so is Igor Ivanovich," said a person briefed on the negotiations, referring to Mr Sechin. "Igor Ivanovich is not a guy who will be bullied by the words of Mr Kadyrov."

Another person close to Rosneft said the clash had escalated so much that there was a need to investigate whether there was "a Chechen connection" in last Monday's bomb attack in St Petersburg, which killed 14 people.

Meanwhile, Vyacheslav Volodin, a former Kremlin aide who became Duma speaker last year, is trying to strengthen the lower house of parliament against the Kremlin. Mr Volodin, a potential presidential contender in the future, is also trying to reinforce his position within the Duma, seizing more control over drafting laws.

Pro-Kremlin opposition parties are also seeking to carve out more space. The Communist party has threatened to walk out on Mr Medvedev's annual government report on April 19 unless the prime minister explains the corruption allegations.

In itself this reflects how Mr Navalny's standing has been boosted. According to pollster Levada, his level of public recognition has risen 8 percentage points over the past month to 55 per cent, 20 percentage points higher than when he led street protests in Moscow in 2012. Among those who know Mr Navalny, 18 per cent say they might vote for him, up from 10 per cent last month.

But Ms Stanovaya believes significant political changes remain a long way off. "They will only happen when you start seeing an open split in the elites," she says.

In 2012 Alexei Kudrin, an economic adviser to Mr Putin and former finance minister, appeared at rallies led by Mr Navalny, and some business leaders supported the opposition. Those protests ended with a government crackdown which landed several activists in prison.

Today, the willingness to protest may be too nascent, and Mr Navalny too weak, to convince members of the political elite to join. Ms Stanovaya says: "Until that happens again, a lot more time is needed for dissatisfaction to gradually accumulate."