AT MITAD DEL MUNDO (“Middle of the World”), a park in an Andean valley outside Quito, Ecuador’s capital, a stone monument marks the line of the equator. Just a couple of hundred metres to the south rises a striking new building clad in silver and black glass, its two cantilevered wings describing a U. It is the headquarters of the South American Union, or Unasur, opened last year.

The host government of Rafael Correa, then flush with oil money, agreed to finance the planned construction cost of $66m. It is a grand architectural statement. But it is still half-empty, and its splendid conference rooms are sparsely used. The building poses a question: just what is the point of Unasur?

Formed in 2008, its origins lie in the South American Community, a Brazilian-inspired push to merge Mercosur and the Andean Community, two would-be common markets, and to develop cross-border infrastructure linking the countries of South America. Under the influence of Hugo Chávez, Venezuela’s socialist strongman, the group changed both its name and its purpose. It shed its economic mission in favour of “political co-operation”. The more or less explicit aim was to displace the Organisation of American States (OAS), whose members include the United States and whose headquarters are in Washington.

Unasur has set up ministerial councils on issues such as defence and health. It has dispatched a dozen missions of electoral “accompaniment”, which are less intrusive and rigorous than the observers sent by the likes of the OAS or the European Union. It facilitated talks between government and opposition in Bolivia in 2008 and in Venezuela last year. And it blessed, without investigation, the narrow victory of Nicolás Maduro, Chávez’s heir, in Venezuela’s presidential election of 2013, a result questioned by the opposition.

Ernesto Samper, a former president of Colombia who became the organisation’s secretary-general last year, says Unasur reflects “a political scenario” in which most South American leaders are “socialist, left or progressive”. Its job is to promote three goals: keeping South America a region of peace, avoiding “democratic ruptures” and defending human rights, understood to include “socioeconomic rights” and the fight against poverty and inequality. Thus the group’s “democratic clause” is not linked to respect for the separation of powers, but rather to “the real validity of social rights”.

To its critics, that looks like an apology for the autocratic regimes of the left in Venezuela, Bolivia and Ecuador, which have seized control of their countries’ courts, electoral authorities and other formally independent institutions. “None of them is prepared to stand up to Venezuela,” says José Antonio García Belaunde, a former foreign minister of Peru. The scope for political co-ordination is minimal, he adds, because South American countries agree about so little. “They don’t share a mission or a vision.” In practice, the seeming left-wing consensus to which Mr Samper refers conceals big differences of outlook.

Its defenders argue that, by eschewing public criticism of member states, Unasur manages to keep open doors that would otherwise be closed to dialogue. Brazil, for example, sees Unasur as “a low-cost, low-maintenance forum” to prevent disputes in its continent from getting out of hand, according to Matias Spektor of the Fundação Getulio Vargas, a think-tank.

Unasur now faces the biggest test of its short life. If previously reliable opinion polls are to be believed, Venezuela’s opposition should easily win a parliamentary election on December 6th. It is not hard to see why: thanks to Mr Maduro’s mismanagement, incomes are plunging, many goods are in short supply and the health service is collapsing. Since the regime has jailed some of its leaders and barred others from standing, the opposition fears that the government will steal the election. Mr Maduro has refused an offer by the OAS’s new secretary-general, Luis Almagro, to send observers.

Unasur claims credit for persuading the government to fix a date for the election (though others, including the United States, which has been holding sporadic talks with Venezuelan leaders since April, also pushed for this). It plans to send a mission of officials from the continent’s electoral authorities ahead of the poll. But how robust will it be?

There is still time for Unasur to staff its mission with people of recognised independence and clout. Mr Samper should seize it. If Unasur ends up whitewashing electoral fraud, its fate will be to join the long list of Latin American organisations that eke out a bureaucratic half-life of irrelevance. The trouble with “political scenarios”, after all, is that they can change.