Chile votes in November to choose a new president and parliament, but there’s a sudden uncertainty about who the contestants will be after centre-right nominee Pablo Longueira withdrew yesterday, citing clinical depression. (A subject I know little about, but which I can’t let pass without pointing to this brilliant First Dog cartoon.)

Longueira was himself the second choice of his party, the Independent Democratic Union (UDI), which had initially chosen Laurence Golborne; he was obliged to stand down due to financial scandals. Longueira became UDI’s candidate in his place, and earlier this month he won a narrow victory in primary elections, defeating the candidate of UDI’s coalition partner, National Renewal, to become the presidential nominee of the broad centre-right alliance, Alianza.

Now Alianza again needs to find a candidate: it may turn to National Renewal’s Andrés Allamand, or there may be a new UDI candidate, such as Labor minister Evelyn Matthei. Or both parties may run separately in the presidential race – voting is by a two-round system, with the runoff on 15 December if required, so splitting the vote in the first round should not be a major worry.

National Renewal, the party of incumbent president Sebastián Piñera (who is constitutionally barred from seeking consecutive terms), is the more centrist partner in the coalition, so Allemand may well be a better bet in the election. But the consensus view is that any centre-right candidate faces a hopeless task in trying to beat the centre-left’s candidate, former president Michelle Bachelet.

Bachelet, a popular and successful president who left office at the beginning of 2010, has enjoyed a commanding lead in the opinion polls; one poll last month credited her with 51% support against just 11% for Allemand and 7% for Longueira.

Since the defeat of dictator Augusto Pinochet in a 1988 referendum, Chile has been mostly ruled by the centre-left, although its candidates have been studiously moderate and avoided any evocation of the radicalism that originally led to Pinochet’s coup. Piñera, who narrowly defeated Christian Democrat Eduardo Frei, has been the first modern centre-right president, and has also tried to present as a moderate – he says he voted against Pinochet in the 1988 referendum.

But Piñera’s administration has not been a success; economic inequality is a persistent issue, and the president seems out of touch with his country’s relatively liberal majority, especially on such issues as abortion and same-sex marriage. Longueira, who was a loyal Pinochet supporter during the 1980s, is even more of a conservative.

Assuming Bachelet wins, it will no doubt be hailed as evidence of Latin America’s continued drift to the left. But that obscures the major differences between her basically centrist position and the radical leftism espoused by Bolivia’s Evo Morales and Ecuador’s Rafael Correa. (Brazil and Argentina generally sit somewhere in between.)

Chile has always been something of an outlier in South America; it was a stable developed democracy for most of the twentieth century when its neighbors were plagued by coups and civil conflict. That’s a major reason why the Pinochet era was such a traumatic experience, while similar dictators elsewhere attracted much less notoriety.

If at the end of the year it again transfers power peacefully from one side to the other, that will be another demonstration of Chile’s maturity.