A broad investigation into corruption at Petrobras , Brazil ’s state-owned oil company, widened on Wednesday with the arrests of a sitting senator and a billionaire investment banker who is one of the country’s top finance executives. The federal prosecutor’s office said in a statement that Senator Delcídio do Amaral, a member of the governing Workers’ Party and an important ally of President Dilma Rousseff , had been arrested in Brasília on Wednesday morning. Ms. Rousseff’s popularity has already eroded since her re-election in October of last year because of a prolonged recession and the Petrobras scandal. There have been calls for her to resign, and the Amaral arrest is likely to complicate her efforts to govern and move economic proposals, including unpopular austerity measures, through Congress. It is also likely to deepen the political crisis here with many wondering if she will be forced […]