Last week, I visited Kiev’s Maidan — “Independence” square. It had something of a street festival feel, but there was also the sense that violence would soon strike.

Barricades of old tires and garbage bags filled with snow protected the ramshackle booths and tent cities erected by pro-democracy groups from around Ukraine. Oil-drum fires helped beat back the brutal cold, but at least the police were leaving the protesters alone.

That ended Tuesday. Riot police stormed the encampment. The barricades went up in flames. People died. And the worst is yet to come.

How different from the Orange Revolution 10 years ago. The crowds then were huge and exuberant, filled with hope that positive change was on the way. It turned out they were naive.

Today’s smaller groups of protesters — serious, calm and grimly determined — are different. They know they are in a bloody fight over the long haul.

Last week, amid the smoke of burning tires, little shrines dot the Maidan. Votive candles flickered under the photos of mostly young faces — those who have already fallen — killed or “disappeared” by President Viktor Yanukovych’s goons. After Tuesday, there will be more shrines.

These protesters are risking it all to break the grip of Mr. Yanukovych’s rapacious Mafia-like “family” (run by his son, Oleksandr) and his patron — Russian President Vladimir Putin.

Under Mr. Yanukovych’s rule, economic freedom has plummeted. Ukraine’s rating in the Index of Economic Freedom is now the worst in Europe and among the lowest in the world. In this repressed economy, corruption is rampant and investment rules are opaque — just the way bullying oligarchs like it.

Tired of Mr. Yanukovych’s corruption and sickened at the prospect of being under Moscow’s thumb once again, Ukrainians said, “Enough.” And once again, Maidan square filled with protesters. The older ones have experienced the oppression of a centrally planned Soviet economy. They do not want to go back.

They also have bitter memories of the “Bloodlands” days of the 1930s when millions of their ancestors were killed or starved to death by Josef Stalin, and then millions more were exterminated by the Nazis. Even Russian-speaking Ukrainians in the east do not want to resurrect the bad old days.

The attack came just one day after Russia delivered $2 billion to shore up Mr. Yanukovych’s tottering government. But the violence probably won’t really intensify until after the Olympic torch is snuffed out in Sochi this weekend. Once world attention moves outside the region, Mr. Yanukovych can send his storm troopers back into Independence Square (and other dissident encampments throughout the country) to finish the job they started before the Olympics began: cracking skulls and imposing an authoritarian state in the name of “law and order.”

If Mr. Putin gets Ukraine back into Russia’s orbit, where will he stop? Will he go ahead and take the rest of Georgia? Grab Azerbaijan? Destabilize Moldova? Threaten the Baltic States?

Former Georgian President Mikheil Saakashvili wrote in The Wall Street Journal last month that the West still has the time, and the means, to save Ukraine. The U.S. and Western European countries should sanction the Ukrainian leaders and oligarchs who orchestrated the crackdown, freezing their Western bank accounts and canceling their visas.

President Obama must work urgently with our European allies to take a firm and unified stand against Mr. Putin. He must look him in the eye, and he must not blink. And he must do it now.

 - James M. Roberts is a research fellow in the Heritage Foundation’s Center for International Trade and Economics