Ms Rousseff does not face charges of involvement in the Petrobras corruption scandal — unlike many of her peers in Brasília. That is despite the fact she was chairwoman of Petrobras at the time. Rather, she faces charges that her administration fudged the government budget in order to boost spending ahead of her 2014 election.

The size of that budgetary fiddle is not insignificant, worth perhaps as much as 1 per cent of gross domestic product. Nonetheless, it is a technical charge. It is also a proxy for the wider popular disdain most Brazilians feel — about the incompetence of her administration, the gross corruption that is being unveiled by the Petrobras probe and the country’s worst recession since the Great Depression. According to recent polls, 61 per cent of Brazilians support Ms Rousseff’s impeachment.

The real crunch happens on Sunday, when the Chamber of Deputies votes on whether to go ahead and send the matter to the Senate for trial. That vote requires 342 votes out of 513 to pass. Over the past few weeks, Ms Rousseff and her allies have scrambled to buttress the government’s increasingly fragile coalition and so protect her position. But the vote remains too close to call. If the motion is approved, the Senate is widely expected to follow suit. If the vote fails, there the matter will rest — at least until other charges come to light.

Brazilian markets have rallied whenever the chances of Ms Rousseff’s ouster have increased; the Bovespa stock market index is up 17 per cent this year. What is less clear is whether what might follow Ms Rousseff’s possible departure will be any better than the present situation.

If she is forced to step down, vice-president Michel Temer would assume the presidency. But Mr Temer faces similar charges of budget fiddling as Ms Rousseff does — 58 per cent of Brazilians think he should be impeached too. If that happens, the head of the lower house, Eduardo Cunha, would become president. But Mr Cunha in turn faces charges of money laundering and of receiving kickbacks from state-run Petrobras.

Brazil’s streets are now occasionally clogged with pro- and anti-impeachment protesters. In Brasília, Ms Rousseff and her Workers’ party are fully deploying the black arts to remain in power — as are their opponents. Claims by the government and its allies that the impeachment process is a thinly disguised coup, while exaggerated, have inflamed passions further. It is already a messy process with an uncertain outcome. It will probably get messier still.