KALUGA, Russia — Russian opposition leader Alexei Navalny is about to walk on stage at a rally in Kaluga, a provincial city about 100 miles southwest of Moscow, when tumult breaks out at the entrance.

See also: The tabloid king who shapes how Russians see the world

A rowdy group of a dozen men from the pro-Kremlin National Liberation Movement, flanked by 30 or so hired young thugs in sportswear, is arguing with security to let them in. One man's T-shirt reads "Fuck USA." Another man sports a shirt with an image of the former Soviet dictator Josef Stalin. He holds a sign saying, "Navalny, get out of Russia," loudly shouting that the opposition figure is a "spy for America!"

Things are getting heated when a voice suddenly bellows from the loudspeakers: It's Navalny. And rather than let the guards push the men away, he invites the rabble-rousers in.

A man donning a Stalin t-shirt holds a sign that reads "Navalny out of Russia," referring to Russian opposition leader Alexei Navalny, during a rally in Kaluga, Russia, June 11, 2015.

For the first 15 minutes of his speech, as hecklers shout themselves hoarse, Navalny can barely get a word in. At some point, someone in the crowd hurls a red, white and blue, star-spangled dildo at him.

Navalny appears unfazed by the vitriol and objects thrown his way. But as soon as the men stop catch their breath, he strikes back.

One by one, he rips apart their poorly argued claims, masterfully shutting them down. The audience erupts in applause, delighted by the verbal sparring.

There is no more heckling. Everyone now listens to what he has to say about Russian President Vladimir Putin, "a man desperately trying to become an eternal emperor," a "liar" who is "destroying Russia."

Russian opposition leader Alexei Navalny speaks during a rally in Kaluga, Russia, June 11, 2015.

Until recently, Navalny couldn't leave Moscow. Since February 2013, the 39-year-old lawyer, anti-corruption campaigner and sharp-tongued Kremlin critic had been under house arrest, banned from using the telephone or the Internet. (He was still able to publish messages on his popular blog and on Twitter with the help of his wife.)

"I watched many of the top 250 films during my house arrest," he says. "The hit for me under house arrest was Grand Theft Auto 5."

Navalny first shot to prominence a few years ago when he began publishing evidence of high-level corruption within the Kremlin, exposing the hidden estates and foreign bank accounts of Putin and his inner circle. During the winter of 2011, he led tens of thousands of Russians in protests against government corruption in Moscow.

Charismatic and outspoken, Western-leaning but nationalistic, Navalny captured the hearts and minds of hipsters and housewives who hoped the handsome, blue-eyed leader could become Russia's next president.

Russian security forces eventually quashed the demonstrations and Navalny, who was seen as the most threatening opponent to the Kremlin, found a target on his back. Russian authorities accused him of embezzlement and threatened to throw him in prison. Surprisingly, he was given a suspended sentence and allowed to run in Moscow's mayoral elections in September 2013.

Russian opposition leader Alexei Navalny alongside protesters in Moscow on Dec. 30, 2014. Image: Evgeny Feldman, Mashable

Despite a vicious smear campaign by the state-run media, he was able to rally Muscovites to the ballot box, winning 27% of the vote.

But a lot has changed in these past two years.

Boris Nemtsov, a prominent fellow opposition leader, has been assassinated — steps from the Kremlin.

Fellow Russian opposition leader Alexei Navalny pays his respects to Nemtsov.

Under pressure from authorities, many of Navalny's financial backers have dropped out of politics or fled to the West.

Worse yet, the Kremlin's Internet censorship laws has made it increasingly difficult for Navalny to reach his digital-savvy support base. And his brother Oleg has been imprisoned.

"Of course I feel guilty," says Navalny, speaking with Mashable in Kaluga after the rally. "It's obvious that my brother is in jail because of me. And not only him, a few other people are, too. He knows it, I know that. That's hard. The Kremlin found a painful spot."

Alexei Navalny inside the Moscow courtroom on Tuesday stands near a temporary holding cell where his brother, Oleg, who was sentenced to three and a half years behind bars, awaits his transfer to prison, Dec. 30, 2014.

Not so long ago, it looked like Navalny might dislodge Putin from the Kremlin. Today, that seems like a far-fetched dream. Navalny's backers among Moscow's intelligentsia, now seem beaten down and apathetic.

Russia's involvement — more or less covertly — in the conflict in neighboring Ukraine, has given rise to a hyper-nationalism in which any opponent of the government can be charged with being unpatriotic.

"When the war began, the main mood among this class was: 'We're going to fight against it,'" Navalny says. "Now the common opinion is that we can do nothing, we should emigrate or pull away from this all."

Russian opposition leader Alexei Navalny speaks to Mashable after a rally in Kaluga, Russia, June 11, 2015.

And he wants to make something clear about Ukraine.

"I'd like to explain to Americans that all this bullshit with the war — it's not what the Russian people want," he says. "It's what a man who is desperately trying to become an eternal emperor wants."

With parliamentary elections set for later this year, Navalny is trying once more to dethrone Putin. But he is fighting an uphill battle.

Putin's popularity at home is at its highest ever in his 15-year rule. A recent poll showed 88% of Russians trust the president's foreign policy decisions.

Vladimir Putin, center, holding a photograph of his father in his naval uniform, marches with a vast crowd to Moscow's Red Square in celebration of Victory Day, May 9, 2015. Image: Ivan Sekretarev/Associated Press

Navalny had hoped Russia's elite, slammed by Western sanctions for their support of Putin and the war in Ukraine, would overthrow the president in a coup d'état.

"There was a contract between the elite and the authorities — 'don't touch politics and we won't touch you' — and it's over now," says Navalny.

But instead of turning on the president, the elite seems to have coalesced around him. Navalny blames "misguided" sanctions from Western governments. A more effective approach would be to create a far-reaching blacklist of Russia's "party of war," he says, "against the thousands of elites who make decisions and do propaganda."

But the U.S. and especially the European Union have shown little interest in doing that. And without their help, the only way to change goes through the ballot box.

"Our answer to this is elections," he says.

Russian opposition leader Alexei Navalny signs an autograph over the face of Russian Railways president and Putin ally Vladimir Yakunin after a rally in Kaluga, Russia, June 11, 2015.

That is, if the government will allow the opposition to participate. There is talk of the government pushing elections forward — from December to September — because it would produce better results for pro-Kremlin parties. "People have been forced to believe that without Putin everything would just fall apart. [But] if one day we wake up and Putin is gone, there won't be a power vacuum. There are old apparatchiks who are now plotting from their sofas," Navalny says.

If Putin vanishes, he adds, nothing will change "except more space will open for positive things to happen in Russia."

Navalny says he has faith that ordinary, working-class Russians, who in the past made up the Putin base, eventually will come around to the side of the opposition. Show them how elites are robbing them to bankroll their own lavish lifestyles, and eventually they'll turn, he argues.

"Everybody wants [political change], even those people shouting at me at meetings — they want it too," he says.

A group of about 300 people listens to opposition leader Alexei Navalny speak at a rally in Kaluga, Russia, June 11, 2015.

After the rally, Navalny ponders the day.

"I'm standing here on a stage in Kaluga and some psychos are shouting at me, and all I'm thinking is: 'Jeez, the river, the sun, the fresh air!' It's useful to experience imprisonment in some way; you start to value simple things."

Today, he says, someone gave him an idea for a good campaign slogan: "Honesty will break this political system."

"The thing is, I don’t have to tell people anything especially convincing," he says. "I tell people simple facts. Most of the people who came to listen already know them."