Jair Bolsonaro could be eliminated from the 2026 presidential race if a court decided he broke the law with his unproven allegations against the voting system.
The Superior Electoral Tribunal (TSE) in Brasilia is trying the far-right former president on charges he abused his office and misused state media when in July 2022 - three months from elections he would go on to lose - he convened foreign diplomats for a meeting at which he insisted Brazil's electronic voting machines were susceptible to large-scale fraud.
Bolsonaro, 68, did not attend the trial. He will be following it from the southern city of Porto Alegre, where he will be holding political meetings, his press office told the news agency AFP.
At the July meeting in the presidential palace, which was broadcast live on public TV, Bolsonaro spent nearly an hour making his case to the assembled ambassadors, armed with a PowerPoint presentation but no hard evidence.
Prosecutors say the event violated electoral law, given that it was held during the polarizing campaign for the October 2022 elections, which Bolsonaro narrowly lost to his leftist arch-rival, now-President Luiz Inacio Lula da Silva.
Insiders say Bolsonaro will almost certainly be convicted, incurring an eight-year ban on running for public office.
The ex-army captain reiterated Wednesday that he had done nothing wrong.
"There was no criticism or attack on the electoral system" at the meeting, he told journalists.
"I simply explained how elections work in Brazil."
Further hearings have been scheduled for June 27 and 29 if necessary and the case could be extended even longer.
Bolsonaro can appeal to the Supreme Court if convicted.