PMDB, Mr Barbalho last month responded with a demand that Congress should set up no fewer than three special committees to investigate his foe.

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Former president Jose Sarney, whose PMDB party is one of the biggest members of her coalition, was re-elected head of the senate for the fourth time.

BBC: Brazilian clown Tiririca takes elected seat in congress

The PMDB's barons were already displeased with what they regarded as a meagre clutch of ministries and other important jobs in Ms Rousseff's government, but had hitherto toed the line.

ECONOMIST: Brazil's president