Giorgi Margvelashvili’s victory in Georgia’s presidential election Sunday was the voters’ latest rejection of Mikheil Saakashvili, the leader of the 2003 Rose Revolution. Last October, Mr. Saakashvili’s opponents won control of Parliament and the prime minister’s office. Now one of their candidates will succeed him in the presidency as well.

International observers judged the voting and the campaign to be perhaps the fairest since Georgia gained independence in 1991. But there are legitimate concerns that the elections could now be followed by prosecutions of Mr. Saakashvili and his defeated followers.

Since Mr. Saakashvili’s opponents won control of Parliament, more than 11 former ministers or top officials of his government have gone on trial or faced charges ranging from theft, bribery and embezzlement to authorizing excessive use of force against demonstrators and prisoners. Former officeholders should be accountable for illegal conduct, but it will be important for the new government to dispel the impression of wholesale prosecution of a defeated political party. These trials must be held in strict accordance with international judicial norms. The European Union, with which Georgia seeks a vitally needed trade agreement, should use its leverage to insist on this.

The election was also a victory for Prime Minister Bidzina Ivanishvili, the pro-Russia billionaire who sponsored Mr. Margvelashvili’s candidacy. Constitutional changes next month will shift many powers from the president to the prime minister. Mr. Ivanishvili, who says he will resign from that post, is expected to handpick his successor, giving him behind-the-scenes control of Georgia’s two top offices. Decentralizing presidential powers to Parliament and the prime minister would make room for a more robust democracy, but not so if real power is exercised by an unaccountable billionaire. Mr. Ivanishvili, who made his fortune doing business in Russia, has a fortune of $5 billion, equal to more than one-third of Georgia’s annual economic output.