Brazilian actor-writer-director Petra Costa is known for mining her personal and family history for material. Her first feature, Elena, turned her search for her absent older sister into a deeply evocative documentary about loss, familial love, rivalry and displacement as it flutters between São Paulo in Brazil and New York City.

Costa’s latest documentary, The Edge of Democracy, finds her intersecting the personal and political on an even bigger public stage, and in the process documents a crisis erupting in slow motion at the heart of Brazilian politics. Thanks to extraordinary access to figures at the centre of the story – former leftist Workers’ Party presidents Luiz Inácio Lula da Silva (AKA Lula) and Dilma Rousseff, as well as rightwingers Michel Temer and current president Jair Bolsonaro – Costa manages to craft an intimate primer about the state’s descent into populism and the fraying of the country’s democratic fabric.

As luck would have it, Costa is well placed to understand both ends of the spectrum. Her grandparents made their fortune in the construction industry, which propped up the likes of Temer and Bolsonaro (and continues to do so), and her Marxist parents went to prison because of their opposition to the military junta that once controlled the country. At one point, Costa observes her mother’s warm first meeting with Rousseff; both women were held at the same prison, although not at the same time, and have much in common.

Throughout, Costa’s voiceover adds shape but doesn’t intrude excessively and lets the powerful compilation of original and archive footage, material shot on the ground in the middle of riots and by drones soaring hundreds of feet above Brasilia, tell the story. That continual contrast between up close and in the fight and soaring high above is mirrored throughout by the film-maker’s perspective, always simultaneously part of the story and watching from a distance.