MOSCOW, Russia – Today, tension grips the streets of Moscow. In what some foresee as the next Facebook revolution, tens of thousands of Russians are rallying in the biggest protest ever against Vladimir Putin.

It was not supposed to be like this. Until recently, Putin was confidently gearing up for a brief, triumphant cakewalk to the Kremlin in presidential polls slated for March 4, 2012.

Then everything changed last weekend. Millions of voters unexpectedly rejected Putin's United Russia (UR) party. Hundreds of credible reports emerged of fraud and vote-rigging on behalf of the party. Since then, panicky Russian authorities have mishandled a wave of street demonstrations in Moscow and other cities.

And now, Putin's prospects are looking quite different. Russia’s once-invincible strongman increasingly appears to be up against the ropes, staggering to get his bearings.

"In just a few days, the situation has changed dramatically," says Mikhail Kasyanov, co-leader of the banned liberal Party of People's Freedom.

"The arrests and beatings of peaceful protesters, who are protesting against obvious electoral fraud, illustrate that he is not taking this as a lesson. This will only inflame the public mood. What we are witnessing is the first crack in the wall, the beginning of the end for the Putin regime," says Kasyanov, who was Putin's prime minister during his first term as president a decade ago.

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In last week’s state Duma elections, Putin's United Russia lost its former two-thirds majority, barely eking out a 50 percent win. The angry legions instead voted for the handful of tame opposition parties permitted on the ballot.

Starting on election night, Russia's social media networks began bustling with activity. Vote-rigging on behalf of United Russia was documented in hundreds of eye-witness accounts, cell phone videos and photos.

At a Moscow press conference, a group of opposition parties revealed their own survey of more than 100 Russian polling stations, alleging that Putin's party may have won only about a third of the votes. United Russia may have even been out-polled by the Communist Party — which official results accorded just 19.2 percent.

Russian authorities appeared blindsided on the first post-election evening. About 10,000 Muscovites, summoned via social media, suddenly converged on a downtown metro station chanting anti-Putin slogans and denouncing the "dirty victory" won by United Russia. Heavily armored riot troops blocked them from marching to the Kremlin. About 300 were detained, and several leaders later handed 15-day prison sentences.

In subsequent days, smaller flash mobs continued to appear in downtown Moscow, St. Petersburg, Samara and Rostov-on-Don, protesting the alleged vote fraud. Hundreds more were arrested, and the Kremlin appeared to have no plan to deal with the unrest other than stepped-up police measures.

"Putin regards this situation as very dangerous," says Sergei Markov, a former United Russia deputy and sometime Kremlin adviser. Markov abruptly left United Russia after the election, but says he will support Putin in his presidential election campaign. "(In Putin's circle) there are intensive discussions underway about what to do. It's clear to Putin that he needs to renovate his methods, and appeal to people in new ways. This is a work in progress," Markov says.

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So far Putin's response has been twofold.

Like Markov, he is apparently molting his now-toxic United Russia party — a political vehicle that has been virtually synonomous with Putin through its decade-long existence.

Instead, last week he opted to file his presidential candidacy papers as the representative of the United Civic Front, a broad movement of public organizations and well-known supporters that he set up last Spring after public opinion surveys began noticing growing public disaffection with UR. In one poll last summer, over a third of Russians said they identified their feelings about the ruling party with the phrase "party of rogues and thieves," while just 20 percent said they believed it was a force "that works for the benefit of society."

"It's not a coincidence that Putin has ditched United Russia, reorganized his campaign and named (popular film director) Stanislav Govorukhin as chief of his election headquarters," says Andrei Piontkovsky, an expert at the official Institute of Systems Analyses in Moscow. "The thing is, United Russia was caught red-handed in massive manipulations and vote-rigging, and everybody knows it. Putin doesn't want to be chained to that."

Putin's second reaction, largely for domestic consumption, has been to blame foreigners and their alleged domestic agents for the week of unrest on the streets of Moscow and other large Russian cities. Experts say this plays to the anti-intellectual instincts and xenophobic inclinations of many in Russia's vast, conservative hinterland. It also reflects Putin's fears of a "colored revolution" similar to the anti-Moscow upheavals that struck the post-Soviet states of Georgia, Ukraine and Kyrgyzstan early in his first presidency.

Speaking to a meeting of supporters last week, Putin declared that criticism of Russia's election by US Secretary of State Hillary Clinton sent a "signal" to pro-US agitators to take to the streets, and that signal was heard and acted upon.

He said protest leaders were operating "in accordance with a well-known scenario and in their own mercenary political interests. ... It is unacceptable when foreign money is pumped into election processes. We should think of forms of defense of our sovereignty, defense from interference from abroad," he added.

Opposition political leaders vehemently deny any foreign connections. It is true, however, that some non-partisan NGO's, such as the grassroots election monitoring organization Golos receive some funding from international foundations and government agencies.

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"What we see in action here is Putin the demagogue, the populist," says Yury Korguniuk, an expert with the InDem Foundation, an independent Moscow think tank. "He may believe this himself, but he also understands how useful it can be to blame the foreign enemy. It is also a warning that protesters may face much tougher penalties if they keep coming out into the streets."

Some experts insist that Putin's public popularity remains strong, and that by separating himself from the tainted United Russia Party and reinventing his political appeal, he can still pull off a strong election victory in March.

"The Putin factor remains the most important feature in Russian politics; he was the motor of United Russia's previous electoral successes and not vice versa," says Alexei Pushkov, a popular Russian TV personality and president of the Council on Strategic Priorities, an independent Moscow think tank.

"There is no opposition figure waiting in the wings who can challenge him. But he needs to renew his political base by putting new people at the helm, embracing new policies, pledging less corruption, less bureaucracy and more social justice. That's what the public mood will respond to," he says.

But others argue that from the moment Putin decided to shoulder aside incumbent President Dmitry Medvedev and seek an unprecedented third term as Russia's supreme leader, in a carefully stage-managed moment at a United Russia convention last September, he put himself on a collision course with public opinion.

"There were many people who were willing to put up with corruption in his circle, because they believed that Putin himself was disinterested and unselfish," says Gleb Pavlovsky, head of the Foundation for Effective Politics in Moscow and a Kremlin strategist during Putin's first two presidential terms.

"But when Putin announced he was running for a third term, he lost aura of invulnerability and his moral charisma was shattered."

