Supreme Soviet Chairman Anatoly Lukyanov, standing, talks with Boris Yeltsin, Russian Federation President while Soviet President Mikhail Gorbachev, right, listens during the morning session of the Congress of People’s Deputies of the USSR at the Kremlin, Moscow in 1990. (AP Photo/Boris Yurchenko) (Boris Yurchenko/AP)

Stephen Sestanovich, a Columbia University professor and senior fellow at the Council on Foreign Relations, was U.S. ambassador-at-large for the former Soviet Union from 1997 to 2001.

Twenty-five years ago this week, a group of Politburo hard-liners launched a coup against Soviet leader Mikhail Gorbachev. The effort to depose him provoked a gigantic popular protest and collapsed in just three days. With the failure of the coup, the communist system itself began to unravel. “The 20th century” — so claimed Boris Yeltsin, Gorbachev’s rival, rescuer and eventual successor — had “essentially ended.” People power had defeated the Soviet state.

Today, an angry populism is again the driving force of politics in much of the world. We can better understand its sources, the problems it poses and, yes, its continuing promise, if we remember both how Yeltsin succeeded and why he finally failed.

Before the coup, many observers — Americans and Russians alike — saw Yeltsin as a crude demagogue making life difficult for the thoughtful, gradualist Gorbachev. His radical demands, they feared, would only mobilize conservatives and divide reformers. Too-rapid pressure for democracy would activate ethnic passion (“suicidal nationalism,” President George H.W. Bush called it).

Yeltsin was a demagogue, but this label missed his real achievement. He had become the leader of an opposition that energized nationwide resistance to the coup. Two months earlier, Yeltsin had won a landslide victory to become president of the Russian Federation. He was the only Soviet politician with a true democratic mandate, and coup plotters hesitated to arrest him. He made himself into a popular hero.

Official Washington, of course, saw Gorbachev as the driver of reform, but it was Yeltsin who kept the pressure on him. He gave advocates of change somewhere to turn whenever Gorbachev retreated from radical ideas (which was often). During the coup, Yeltsin also provided its opponents with a physical rallying point. That famous tank he climbed onto was, with its friendly crew, parked right outside his office.

Perhaps most important, Yeltsin’s strong anti-communist rhetoric turned out to moderate ethnic passions rather than inflame them. Throughout Eastern Europe and the (soon to be dissolved) Soviet Union, nationalist conflict was marginalized wherever popular mobilization revolved around anti-communist ideas. Nothing demonstrated this connection more clearly than the violent break-up of Yugoslavia. Because the Yugoslav regime had long since drifted away from Marxism-Leninism, socialist ideology and anti-communism were equally irrelevant. Ethnic grievances — pushed by demagogues such as Slobodan Milosevic in Serbia and Franjo Tudjman in Croatia — took center stage.

Yet if Western governments underestimated the value of Yeltsin’s populism in his challenge to Gorbachev, they also failed to see what would happen if Yeltsin could not make good on his populism after he took power. After the collapse of the Soviet Union in December 1991 — and in eight years as president of the new Russia — Yeltsin regularly sought refuge in anti-communist rhetoric. But it did him less good as time went on.

A demagogue who attains power has to show he can deliver, and Yeltsin did not. Beyond the material hardship his policies produced, critics charged that he let new scoundrels replace the old ones. The populist who railed against insider privilege in the Soviet system allowed gross abuses of power on his watch. Ordinary citizens who backed Yeltsin’s call to tear down old institutions gradually came to favor their revival. Yeltsin didn’t just pick Vladi­mir Putin as his successor; he made it easy for Putin to become popular. As the new president, Putin took on the enemies that he claimed were pushing Russia around — corrupt oligarchs, Chechen separatists, foreigners (and especially Americans). Having failed to act like a populist president, Yeltsin gave Putin the chance to play the role.

The coup against Gorbachev and its aftermath have their echoes today. The 1991 populist overthrow of Soviet communism was not so different from the 2014 populist overthrow of the Yanukovych regime in Ukraine. Each was a national uprising against a system seen as corrupt and undemocratic; each offered new leaders a mandate for root-and-branch transformation.

Despite some real progress, however, Ukraine’s new government has the same flaw as Yeltsin’s — too little reformist follow-through. If Ukraine’s experiment founders, U.S. policymakers are likely to feel the same retrospective remorse that they feel about post-Soviet Russia. Too often, Western governments have made excuses for backsliding. They have treated “populism” as their enemy, not seeing that — as a force for fundamental change — it can be their friend.

European politics today shows how much has changed since the liberal populism of the late 1980s and early ’90s. Populism is now almost everywhere illiberal — thriving on ethnic hostility and exclusion. East European movements and leaders used to denounce a corrupt elite that they said blocked integration into a broad democratic Western community. Today they say real democracy is impossible unless that integration is reversed. In the view of 21st-century populists, only the elite benefit from integration.

It is hard to recall Yeltsin’s populism — anti-communist, liberal, tolerant, forward-looking — without feeling regret for what might have been. But 25 years after the coup, it is not too late to learn its lessons. The first is to recognize the positive mobilizing force of popular frustration. Real conviction and determination generate the kind of support that caution can rarely match. In hard times people trust a Yeltsin rather than a Gorbachev to understand their anger.

The second lesson is not easy to act on but just as important. Over-promising and under-performing give life to populism of a far more dangerous type. Once people conclude that liberalism serves only the privileged, that popular grievances are never answered, that the usual reform simply produces new scoundrels, they take their anger elsewhere.