SOMETHING unexpected happened in Chile’s presidential election last month. In the first round in November, Sebastián Piñera, a centre-right former president who was the favourite, stumbled. He won only 37% of the vote, six points less than the combined tally of two left-of-centre candidates. But in the run-off an extra 1.4m voters turned out for Mr Piñera, giving him a comfortable victory. Many of them had stayed away in the first round. Most were new recruits to Chile’s middle class alarmed by the prospect of a swing to the left under Mr Piñera’s opponent, Alejandro Guillier.

As Latin America begins a series of presidential elections this year against a background of sluggish economic growth and anger over crime and corruption, the Chilean result is a reminder that its middle class is bigger and more influential than ever. But its political impact is far from straightforward. And that is because the term itself requires unpacking.

What is clear is that the region’s middle class has grown. The World Bank assigns this status to people who have daily incomes of $10-50, enough to offer some security. By this measure, 34% of Latin Americans were middle class in 2015, up from 21% in 2003. A further 39% had incomes of $4-10 a day. They were no longer poor but could easily become so again. This rise in income—the result of faster economic growth between 2003 and 2011—went side by side with a big expansion in education and in ownership of durable goods, from computers and cars to wide-screen televisions. Some 42% of respondents to Latinobarómetro, a regionwide poll, describe themselves as being “middle class”.

These “middle sectors” as Ignacio Walker, a Chilean politician and political scientist calls them, are heterogeneous. In the past, Latin America’s middle class was composed of independent professionals and public employees. The new middle class tends to work in the private sector, as managers, technicians or owners of small businesses. They are “aspirational and emerging”, says Mr Walker. Many have benefited from globalisation. Some may work in the informal sector; they think of themselves as self-made. Rather than being genuinely middle class, some simply have more money than they used to.

A large middle class is often seen as a guarantee of democratic stability: with much to lose, it has an interest in property rights, limits on state power and policy continuity. But turmoil can precede stability. Samuel Huntington, an American political scientist, noted in 1968 that “the true revolutionary class” in modernising societies was the middle class, but that it became more conservative as it grew.

It is not clear whether Latin America’s middle class will follow the same trajectory. Historically, it tended to ally with trade unions against oligarchic rule. But it was sometimes counter-revolutionary. Military coups against left-wing governments in the 1970s were backed by a middle class fearful of socioeconomic disorder. There is an echo of that in the support that early opinion polls give among the better-off and better-educated in Brazil to Jair Bolsonaro, a right-wing populist. His supporters blame the Workers’ Party of Luiz Inácio Lula da Silva for an economic slump that slashed living standards and saw a rise in crime as well as corruption. Nonetheless, many of the new lower-middle-class Brazilians love Lula, whom they associate with earlier economic growth and cheap student loans and housing credits.

In today’s Latin America, the new middle classes’ main demand is for better services, from higher education to health care and policing. But that doesn’t necessarily imply public services, or a big state and support for the left. “They oscillate between ‘Let me progress’ and ‘Protect me if I fall,’” says Sérgio Bitar, a Chilean former minister who advised Mr Guillier.

Take Bolivia, where a mestizo middle class has grown under Evo Morales, the left-wing president who has governed since 2006. It has now turned against him. After protests, this week Mr Morales withdrew a new criminal code that was seen as oppressive. In Mexico the middle class twice voted tactically to prevent Andrés Manuel López Obrador, a left-wing populist, from winning the presidency. In this year’s contest Mr López Obrador is striving to appear more moderate. As less extreme candidates emerge in Brazil, its middle class may shun Mr Bolsonaro.

This electoral cycle will show whether Latin America’s middle classes have matured politically. If so, they will vote for candidates of the left or right who offer a well-judged mix of opportunity, social protection and stability. If not, Mr Bolsonaro and his ilk have a chance.