Massive protests calling for the impeachment of President Dilma Rousseff have narrowed her options to fend off political and economic crises and will mean more turbulence for the nation in the months to come, but her ouster remains highly unlikely, analysts said Monday.

Polls showed the Rousseff government’s popularity had already been cut in half before Sunday’s protests, compared to when she won re-election in October, and the sheer size of the challenge facing her was splashed across front pages of newspapers Monday with photos of the surprisingly huge crowds seeking her removal.

Anger over a sprawling corruption scheme sparked Sunday’s marches in more than 150 cities.

Federal prosecutors say they’ve uncovered Brazil’s biggest graft case yet in a kickback scheme at state-run oil company Petrobras, with at least $800 million paid by construction and engineering firms in bribes to politically appointed former executives at the oil company, all in exchange for winning inflated contracts.