Could Sergio Moro bring down his second president?

In March 2016, the Federal Police recorded a phone conversation between then-President Dilma Rousseff and her predecessor, Luiz Inácio Lula da Silva. Federal marshals were tapping the phones of the latter, who was the subject of several criminal investigations. In the 95-second dialogue, Ms. Rousseff discussed Lula’s appointment as her Chief of Staff, a maneuver to grant the former president immunity while he negotiated a way out of Ms. Rousseff’s impeachment proceedings. Hours later, Sergio Moro — then a federal judge leading Operation Car Wash — illegally leaked the recording, triggering major protests across the country and essentially ending any possibility Ms. Rousseff had to avoid impeachment.

Four years later, Mr. Moro could be the key factor in tipping the scales against another president. On Friday morning, he handed in his resignation from his role as Justice Minister, following the dismissal of Federal Police Chief Maurício Valeixo.

In a filibustering speech on Friday evening, Mr. Bolsonaro alleged that the outgoing Justice Minister had tried to negotiate with the president, wanting a seat on the Supreme Court in return for Mr. Valeixo’s removal. However, President Bolsonaro was the one who offered Mr. Moro the seat in May last year.

Mr. Moro said that President Jair Bolsonaro had tried, on numerous occasions, to interfere with federal probes and illegally obtain police reports of sealed investigations into members of his entourage.

Moreover, he claimed the government had published false information on Friday morning’s issue of the Federal Registry. The official gazette stated that Mr. Valeixo had resigned and that the publication had been signed by...