On Aug. 7, Juan Manuel Santos will take office as the new president of Colombia. He will do so after eight years of Alvaro Uribe’s popular, effective and controversial mandate; the last time someone governed Colombia for so long was during the 1950s when strongman Gustavo Rojas Pinilla remained in power for almost a decade.Uribe convinced his countrymen four years ago that reelection was a good idea; he tried to persuade them again this year, and failed. Instead, he anointed a successor, who proceeded to obtain an extraordinary mandate of almost 70 percent of the vote.Antanas Mokus’ remarkable early rise in the polls and the apparent enthusiasm he awakened among young, middle-class, urban dwellers of Bogotá (of which he had been twice elected mayor) and other large cities, fizzled. Why did Santos win such a landslide, and what does his victory mean for Colombia and Latin America?• First, he won because Uribe remains immensely popular, despite corruption, human-rights and intelligence scandals. He has brought relative peace to a country that had been at war for decades — and at a price most Colombians consider acceptable. Kidnappings, homicides, terrorist bombs, hold-ups and crime in general all are way down, the FARC guerrillas have been fatally weakened (not destroyed, however). Cocaine production is not significantly down, but that is seen as a U.S. and European problem. The economy has fared well, despite a predictable dip in 2009.Uribe delivered enough of the goods the Colombian people desired; those he didn’t deliver, he was able to credibly promise were on their way.• Second, that immense popularity turned out to be transferable to Uribe’s hand-picked choice of a successor, if he made the right choice. He did. Santos lacked charisma, was overconfident and, perhaps, made a mistake here and there at the start of his campaign. But he had sterling credentials as a former Minister of Trade, Finance and Defense, as an honest journalist, and as a conservative who has reached out to progressive sectors at home and abroad.Uribe was able to make the case tacitly, and Santos stridently, that this was not the time to change horses in mid-stream. The course to stay consisted in finishing off the guerrillas, maintaining the alliance with Washington, dismantling the remaining paramilitary groups and containing the so-called drug mini-cartels.The real issue now is whether Santos, after his victory, can shift to the center and a more social-democratic approach to Colombia’s problems. When I met him years ago and helped him launch his book on the Third Way in Colombia, he was a convinced disciple of Anthony Giddens and a fan of Tony Blair’s. Their gild has faded, but the need for an analogous option for Colombia is more evident than ever. Uribe has done the heavy lifting; Santos can recenter policy, focus more on economic and social development, together with greater respect for human rights, and become a driver for a modern alternative to Venezuelan Hugo Chávez’s demagoguery and others’ neutrality toward his policies in Latin America.This is both the central challenge confronting Santos as well as the exceptional opportunity he faces. Latin America has fared well the past decade or so. Brazil, Chile and Uruguay, with diverse combinations and sequences of center-left governments, have all seen poverty and inequality diminish, the middle class expand and democracy take serious root.Other countries, such as Mexico and Colombia, have also made significant progress, though less impressively. This difference has made it possible for a harder left, led by Chávez and including the leaders of Cuba, Nicaragua, Ecuador, Bolivia and, to a lesser extent, Argentina and Paraguay, to tout the virtues of radical populism, anti-Americanism and anti-globalization, as well as to flaunt the need to perpetuate themselves in power. As Sebastian Edwards shows in a splendid new book — Left Behind: Latin America and the False Promise of Populism — in the long run this path leads nowhere, but the other path has yet to be fully followed, except in Chile.Latin America needs a successful, progressive and democratic accompaniment to the Chilean example, that can be attributed to an enlightened government of the center-right that tilts to the left, in the same way that Brazil and Uruguay have benefitted from enlightened governments of the center-left that tilted to the right.Latin America also needs a strong voice in favor of the type of regional and international legal regime that truly defends human rights and democracy, the environment, nonproliferation and world criminal justice, over and above the traditional principles of national sovereignty and non-intervention.Santos and Colombia can become that voice, and that accompaniment: they have the talent, the mandate, the foundations and the vision.All they need is the ambition and the boldness to try.Jorge G. Castañeda is Mexico’s former foreign minister, Global Distinguished Professor at New York University and fellow at the New America Foundation.