In the most peaceful revolution since South Africa ended its apartheid regime by electing Nelson Mandela president in 1994, Ukraine has just elected opposition leader Viktor Yushchenko president of the former Soviet satellite republic. The victory comes for the pro-Western leader after a dirty campaign that saw him poisoned and only after hundreds of thousands of demonstrators filled the streets to protest voter fraud. “We peacefully, beautifully, elegantly, and without any drops of blood changed Ukraine,” Mr. Yushchenko told cheering supporters.

What many Westerners do not realize, however, is when Mr. Yushchenko takes the seat of power, at his side will be a tough-minded, savvy, American-raised businesswoman. His wife, Kateryna Chumachenko Yushchenko, is the daughter of Ukrainian immigrants who grew up steeped in the traditions of her ancestral homeland.

Mrs. Yushchenko was raised in suburban Chicago as the daughter of an electrician and a seamstress. During World War II, her parents were forced to immigrate to Germany and work as slave laborers. They came to America in 1956 at the invitation of a Ukrainian Orthodox church. She grew up speaking Ukrainian at home, learning the national dances, and attending a Ukrainian school and an Orthodox church. “My parents felt they had to keep alive the culture and traditions they thought were being suppressed by the Soviet Union,” she told me.

In the late 1980s and early 1990s, she worked in the human rights office of the U.S. State Department. She also worked for the first President Bush in the Treasury Department. But her dream was always to help Ukraine become independent. So after the collapse of the Soviet Union in 1991, she moved to Kiev. Her business degree from the University of Chicago helped her land a job with KPMG, the American international auditing company, and she prospered training the country’s economists in Western practices. She met Viktor Yushchenko when he was part of a delegation of central bankers she brought to Chicago. “He understood free markets, had a firm faith in God, and knew what the right path for the country should be,” she told me. The two married in 1998, and they now have three children.

It is the strong bond he has with his wife that has helped Mr. Yushchenko through the tough campaign, and it will likely be his relationship with her that will help him have a successful presidency. Perhaps the darkest moment for Mr. Yushchenko came this fall when he was poisoned. At first it seemed to be a case of the flu. His wife recalls him coming home one night during the presidential campaign and saying he felt sick. She noticed a strange metallic taste in his mouth when she kissed him. It turned out to be dioxin, a chemical compound found in Agent Orange and a well-known poison.

Mr. Yushchenko has largely recovered, although the poison has left his face disfigured and the government has continued a three-year campaign to discredit him and his wife. After he was poisoned, the state prosecutor opened an investigation into the incident and then tried smearing Mr. Yushchenko by claiming he had a disfiguring case of herpes.

Tape recordings made by a disgruntled bodyguard for President Leonid Kuchma show that the president personally ordered a disinformation campaign against the Yushchenkos. Mr. Yushchenko was portrayed as a fascist puppet of Western bankers and Kateryna as an active CIA agent. She responded by winning a libel judgment against a Russian television station that accused her of disloyalty to Ukraine. But the government has refused to process her application for Ukrainian citizenship.

Now that Mr. Yushchenko is to become president, it’s likely he’ll be able to push through more than his wife’s citizenship application. He helped implement some free-market reforms when he served as prime minister for 16 months between 1999 and 2001 before being ousted by hard-liners in Parliament. Now he has a popular mandate at his back as well as international support, which has only increased with the success of his “orange revolution.” His wife has also proved invaluable by introducing him to contacts in the West.

All this adds up to a rare opportunity for Mr. Yushchenko. Since its independence in 1991, Ukraine’s 48 million people have seesawed between forming greater ties with the West and lurching back into becoming a vassal state of Russia. One out of six people are ethnically Russian. Still, a clear majority of voters now want the corrupt, pro-Moscow clique surrounding outgoing President Kuchma out of the government. Yulia Timoshenko, a charismatic ally of Mr. Yushchenko, says their time is up. She told reporters: “I think the key word for them in Sunday’s exit polls was ‘exit.'”

The challenge will be to move Ukraine toward a free-market economy. Mrs. Yushchenko makes clear that her husband makes all of his own political decisions, but she will no doubt be a valuable asset to him. “She is one of the brightest, most dedicated conservatives I have ever known,” says Bruce Bartlett, a former official in the Treasury Department under the first President Bush. “Anyone who met Kathy quickly discovered that creating a free, successful Ukraine was her primary mission in life, to the exclusion of almost everything else.”

Now the challenge facing Ukraine is to make the leap toward becoming a democratic society truly governed by the rule of law. Mrs. Yushchenko is realistic about the obstacles facing her husband and his team. “[Some] people are making a lot of money off the current system,” she told ABC News. “The last thing they want is for the system to change and for the economy to be a free-market economy where the general population benefits rather than a small group of people at the top.”

Cynics may say that since Ukraine has never been a true democracy, reforming it will be impossible. But those are the same people who never predicted that hundreds of thousands of people would fill the streets of Kiev and other cities and force a new election. Nonetheless it happened. What happens next is now up to Mr. Yushchenko.

Mr. Fund is author of “Stealing Elections: How Voter Fraud Threatens Our Democracy.” To subscribe to the “Political Diary” e-mail newsletter featuring Mr. Fund, please visit www.OpinionJournal.com, from which this column is excerpted. © Dow Jones & Company Inc.