President Vladimir Putin faces a decision over Ukraine that is likely to shape his political legacy as well as the future of Russia's western neighbor, trapped in an East-West battle that has echoes of the Cold War.
President Viktor Yanukovych's loss of power deprives Putin of an ally vital to his hopes of keeping Ukraine, the cradle of Russian civilization, in what he sees as Russia's orbit.
His hopes of building a huge trading bloc, grouping as many former Soviet republics as possible to challenge the economic might of China and the U.S., could be in tatters.
But making a stand over Ukraine, or getting drawn into a new bidding war with the European Union to win sway over the cash-strapped country, would be risky.
Moscow can ill-afford to improve the $15 billion financial bailout package it offered in December. But more forceful measures, such as taking over mainly Russian-speaking areas of eastern Ukraine, would risk triggering a more serious conflict.
Putin is saying nothing for now in public, although he has spoken by phone to U.S. President Barack Obama and German Chancellor Angela Merkel. He was especially keen to stay silent before the end of the Winter Olympics in Sochi.
But the protesters on Independence Square in central Kiev are waiting anxiously to see what he does.
"We all know Putin likes to meddle," said Alexei Tsitulski, a 25-year-old protester from the Crimea. The region used to be Russian territory and was given to Ukraine in 1953 by Soviet leader Nikita Khrushchev, who was from Ukraine.
"If he decides to try to take over regions like Crimea or anywhere else in the east, we will go there to fight. We are not going to let Ukraine be split."
Such comments, echoed by other protesters, underline how high the stakes are as Putin looks for ways to save face in the geopolitical struggle over Ukraine that had appeared to be going his way until the past week.
The U.S. also said on Sunday that sending forces to Ukraine would be a "grave mistake."