How a Brazilian labor party became a far-right stronghold

With five months to go before the October elections, the Brazilian Labor Party (PTB) is focusing on its candidate for the Senate in Rio de Janeiro: Congressman Daniel Silveira — who was recently convicted to almost nine years in prison for threatening to physically assault members of the Supreme Court.

This candidacy may not materialize, as Mr. Silveira’s eligibility remains in question, but it underscores how the party has slid towards the far-right. Besides a possible bid for the Senate, the PTB is pushing for Mr. Silveira to be a permanent member of the Constitution and Justice Committee, the most important in the House.

More than anything, the PTB’s choice of Mr. Silveira is a nod to President Jair Bolsonaro, who elevated a previously irrelevant figure in national politics to make him the symbol of his war against the Judiciary. It represents the latest metamorphosis of a once-massive party now struggling to regain relevance.

The PTB’s origins date back to 1945, when it was founded by former President Getúlio Vargas. As the ‘labor’ in its name implies, the party aimed to defend workers’ rights at a time during which employers...