LONDON – Last week, Alexei Navalny, the recently convicted Russian opposition blogger, lawyer and candidate for the post of mayor of Moscow, posted a provocative item on his site.

It was an open letter addressed to the present mayor of Moscow, Sergei Sobyanin, accusing him of authorizing the theft of pro-Navalny banners from the city’s municipal high rises. “Could you please answer my question?” asked Navalny, 37, tartly. “Why do you, along with your migrant workers for municipal utilities, steal our Navalny banners from the balconies of the residents who have installed them?”

As a statement, it was instructive in more than one respect. It illuminated the confrontational style that has characterized Navalny’s rapid rise as one of Russia’s most visible opponents of President Vladimir Putin and his inner circle. But also, in the reference to “migrants,” it suggested why some harbor deep suspicions about Navalny’s liberal credentials. Beyond all that is the very fact of Navalny, who was sentenced last month to five years in jail on the trumped-up charge of “stealing” a forest in Kirov region, of being free at all and able to run against Sobyanin.

On that last, puzzling point, theories abound, some conspiratorial and some grubbily pragmatic. The corruption sentence, against which Navalny is appealing, would ban him from holding public office if upheld. His chances of beating Sobyanin, in any case, look remote, according to opinion polls.

One plausible theory is that Navalny was released on bail at the prosecution’s request — and for that read, with the Kremlin’s approval — because Sobyanin, having called a snap election for one of the most high-profile public offices outside of the presidency, required a credible opposition foil to claim a veneer of legitimacy.

Another theory posits a split within the Kremlin elite over what to do about the problem of Navalny between the siloviki — Russia’s powerful securocrats — and a more pragmatic group of political strategists who argue that the policy of prosecuting President Putin’s opponents, including dead ones such as Sergei Magnitsky, is a bad one.

Whatever the real reason, for now at least the charismatic and good-looking lawyer, who has brought together skill with social media, personal flair and a sharply populist critique of Kremlin corruption, has had a prominent platform gifted to him by Putin and his allies. If that is a risky strategy for the Kremlin in the long run, it is because it has opened up a political space that may be difficult to shut down.

Navalny’s most striking slogan, charging Putin’s United Russia party with being the “party of crooks and thieves,” was, he admits, a slip of the tongue — uttered during a radio interview in the run-up to the controversial December 2011 parliamentary election, widely considered to have been marred by electorate fraud. For his part, Putin has assiduously avoided referring to Navalny by name, suggesting that he is, perhaps, aware of the blogger’s political potential.

After making his slip, Navalny organized a poll on his blog: “Do you consider United Russia to be the party of crooks and thieves?” Yes, said 97 percent of 40,000 respondents. “From the very beginning, it was clear that the election was going to be unjust,” said Navalny,” but I really wanted to know if one could do any significant damage to United Russia by means of a campaign launched on the internet.”

It was the 2011 election that first brought Navalny high visibility on the domestic and international stages, as he became a lightning rod for the mass protests that followed, leading to his first two-week-long arrest. Used to attracting a few hundred to his rallies, the first big one in Moscow after that election drew an estimated 100,000 people. The following year saw Navalny’s coronation, as the opposition elected its own leaders.

Navalny topped a public online ballot in which 81,000 votes were cast. That was a peak for the opposition’s “white ribboners.”

Navalny’s mayoral campaign since his release on bail has struggled to attract similar crowds. Photographs posted on his blog suggest rallies often attended by a few hundred, seeming to confirm claims that the opposition has lost some of its momentum, on the streets at least.

But then Navalny, since emerging as a political activist 13 years ago, has tended to flourish at a remove from the conventions of Russia’s opposition politics, excluded, as he has been by an undeclared diktat, from state television. Dismissed by Putin party allies as a “dirty self-publicist” and as a “little hamster from the social networks,” he replied publicly in 2011: “Yes, I am a little network hamster! And I’ll gnaw through the throats of these cads!”

It is precisely his sharp, sarcastic, mocking style that has enamored Navalny to his many young supporters.

While Russia is benefiting from an oil and gas boom, runs his message, it is only a corrupt few who have been enriched by the new wealth. He has prosecuted his online campaigns with fearless vim and humor, insisting — with sang-froid even as he listened to his sentencing — that he was unafraid and laid-back about consequences.

Although he had been involved in political activism before, through the liberal Yabloko party, it was the launch in 2008 of Navalny’s blog detailing corruption in state institutions that brought him to prominence. It also allowed him to launch the fund that has supported his efforts. Another novelty, in a country where recent polls suggest suspicion both of Putin’s ruling party and the opposition, is that Navalny is untainted by association with power in the 1990s. As Julia Ioffe, the perceptive analyst of the modern Russian political scene recently noted, Navalny arrived with a fresh pitch.

“Navalny understood that Putin was not Russia’s main problem. Rather, the problem was the post-Soviet culture of greed, fear and cynicism that Putin encouraged and exploited,” she wrote in New Republic. “Navalny carefully distanced himself from the shrill, old-guard western-friendly liberals — “hellish, insane, crazy mass of the leftovers and bread crusts of the democracy movement of the ’80s,” he called them — who simply participated in Putin’s cult of personality in reverse.”

At the heart of his message is a call for free and fair elections, the notion that there is no unique Russian disposition that makes his country prone to corruption, political and financial. It is a pitch as much against those who have chosen the easy route of apolitical neutrality as it is against Putin’s Kremlin machine.

And the success of his blog, as Navalny has pointed out, has had as much to do with what the Russian media would not report as what he would. It is a theme that recurs. Navalny argues that he is not necessarily more popular himself, only that others — notably Putin — are increasingly less so. Despite the sometimes self-deprecating shtick — in sharp contrast to Putin’s self-mythologizing antics — there remains disquiet about what Navalny really represents, behind the caustic put-downs and cool persona.

The reference in his open letter to Sergei Sobyanin to “migrants” — Uzbeks and Asians in this case — was not a solitary slip. While his vision of a future Russia has often been vaguely shaped — as a nebulous “vast metaphysical Canada” — it has been suffused with a strong strand of sometimes xenophobic nationalism.

In an interview with Radio Free Europe, he talked of his “realistic agenda” to develop policies that will prevent ethnic conflict, including fighting illegal immigration, combating ethnically based gangs and bringing order to the North Caucasus.

Although he has fiercely rejected claims made by Engelina Tareyeva, a former colleague in Yabloko, that he routinely used “racial slurs,” some of his remarks have sailed very close. Indeed, he has appeared at rallies next to hardline nationalists, including skinheads, and once appeared in a video where he appeared to compare Caucasians to “cockroaches.”

All of which leads to the question: what next for Alexei Navalny?

Even if, as is expected, he loses the race for mayor of Moscow, some have speculated that he has his eye on a bigger prize in the long run: the presidency itself, which might explain his courting of the nationalist vote.

And Navalny, too, sees the virtue of being pursued through the courts and even jailed. Speaking after his first brief prison spell in 2011 he has said: “My detention has done me good. People who weren’t too fond of me before now feel sorry for me.”

Maybe this explains his odd insouciance over the prospect of five years in jail. This is a country where a corpse can be convicted, a punk band sentenced to hard labor; where elections are massaged and opponents of the president regularly convicted, so investing in jail time might make more sense for the political aspirant eyeing high office, post-Putin, than the business of stumping.

Navalny file: a glance at Putin’s biggest critic

Born: Alexei Anatolievich Navalny on June 4, 1976. He grew up in Obninsk, 100 km from Moscow. He studied law at the Peoples’ Friendship University of Russia.

Best of times: In February 2011 in a radio interview, Navalny framed a critique of Vladimir Putin’s United Russia party that would galvanize opposition, calling them “crooks and thieves,” a phrase that has entered the Russian political lexicon.

Worst of times: His conviction and sentencing on trumped-up charges to five years in jail for “stealing a forest,” although the conviction may turn out to be a blessing for his political career.

What he says: “Sometimes, it seems that there’s a little crazy screenwriter sitting in the Kremlin and occasionally, out of nowhere, he decides to enhance one politician or another.

“In fact, my detention has done me good — people who weren’t too fond of me before now feel sorry for me.”

What they say: “He is the only man who can take all the common hipsters and make them go on to the street. He is a figure who could beat Putin if he was allowed.” — Supporter Anton Nikolayev, quoted outside court by The New York Times.