Lilia Shevtsova, of the Carnegie Russia think tank in Moscow, said: "Yanukovych's behaviour became the crucial factor.

"He is trying to ensure his reelection in 2015. This primary motive has guided his actions.

"He concluded that European integration would not guarantee him victory and decided to fall back on Putin's formula of preserving power."

Since his refusal to commit to Europe and instead opt for Russia at an EU summit in Lithuania last Friday, the president has been surprisingly quiet.

Hundreds of thousands have taken to the streets of Kiev and occupied official buildings.

He has failed to respond in words, except to issue a statement last week saying he was deeply indignant at the riot police attacks on peaceful protesters. But public speaking has never been his strongest suit.

Yanukovych presides over a dysfunctional, deeply divided, highly corrupt, extremely poor country positioned pivotally between Russia's western frontier and the EU's eastern flank.

Parts of western Ukraine used to be Poland and before that part of the Austro-Hungarian empire, while the Russian-speaking east and south belonged to Moscow and remain culturally Russian. There is no national consensus on what the country should be.

A native Russian speaker who learned to speak the country's first language in his 50s only out of political expediency, Yanukovych has long been seen as of the old regime - as Moscow's man.

The balancing act has been tricky and he has had rough moments with the Kremlin.

But as he showed last week, when push comes to shove he is much more comfortable with the politics practised in Moscow.

He feels he can benefit more from standing by Russia than from the systemic reforms that would have flowed as a result of the political association agreement and free trade regime with the EU that he ditched in Vilnius.

"This is a revolutionary situation, in a technical sense," said Andrew Wilson, Ukraine expert at the European Council on Foreign Relations. "His natural instincts are to attack."

It may turn out to be harder to unseat Yanukovych than it was in the orange revolution of 2004-5.

He himself ignited that revolt by trying to steal an election. He lost, giving way to Viktor Yushchenko, who proved an ineffectual president embroiled in persistent intrigues with the then prime minister and fellow revolutionary, Yuliya Tymoshenko.

"Yanukovych risks going down in history as a man who over the past 10 years has twice been deprived of power by the square," said Russia's liberal daily, referring to mass protests in the capital, Kiev.

Yanukovych made a comeback, replacing Tymoshenko as prime minister. He then beat her to the presidency in 2010.

A year later she was in jail. But outside observers, unlike in 2004, gave the 2010 contest a clean bill of health.

In the middle of his five-year term, Yanukovych is clearly in trouble. He has been dogged by allegations of an excessive liking for luxury at a time of economic trouble, with critics focusing on his personal riverside residence of Mezhygirya outside Kiev. A so-called family of influential officials and relatives has grown around him, including Yanukovych's increasingly affluent businessman son Olexander. Equally important is a group of billionaire oligarchs who are believed to have a huge say in decision-making, including the owner of the Shakhtar Donetsk soccer club, Rinat Akhmetov, and energy tycoon Dmytro Firtash.

But how much trouble is the president really in? Can he weather the protests, grind the demonstrators down and rely on his secret police and security forces? Can he also rely on some of the most powerful oligarchs in the country who bankroll him and control much of the media?

Can he depend on Russian President Vladimir Putin to shore him up? And can he secure the loans needed to forestall Ukraine going broke?

In 2004, the security forces split between the revolution and the old regime. Yanukovych has already lost several lawmakers and his chief of staff, Serhiy Lyovochkin, has defected. Together with the energy oligarch and one of Ukraine's richest men, Dmytro Firtash, Lyovochkin controls Ukraine's biggest television station. Firtash is also believed to "own" up to 10 lawmakers who could tip the balance in bringing down the government, if not the president.

Yanukovych is one of several leaders, all strongmen, all relatively popular, all winning elections, and then using their mandates to polarise and divide, reward cronies and punish rivals.

They are control freaks who fear and despise independent institutions and vibrant civil societies. There are similar situations in Russia, Turkey, and Hungary.

The leaders are different, specific to their own cultures, but share many characteristics and employ similar methods of control and coercion, buying loyalty and penalising opposition and resistance. If you are a Russian, a Turk, a Hungarian, or a Ukrainian right now, according to the powerful government chiefs, you are either with them or against them.

In 2004 the orange revolution achieved critical mass, as did the protests in parallel crises in Serbia in 2000 and Georgia in 2003, and managed to topple the old regimes. The Kremlin studied the events closely and learned its lessons. A street victory in Kiev will be a defeat for the Kremlin.

Wilson said the tipping point could have been a vote of confidence in parliament last Tuesday, but a measure calling for the government's resignation was defeated. The failure of the no-confidence vote pushed the battle for the future of Ukraine back onto the streets, where demonstrators and political opposition leaders allied with them said they would not relent until they succeeded in removing the government, including Yanukovych.

"Our demand is impeachment of the president and dismissal of the government," said protester Oleksiy Ivannikov, 35.

"I see no compromises here."