The President's delay in conceding the race has contributed to fears that Bolsonaro will not cooperate with a transfer of power. In the lead-up to Sunday's run-off vote, Bolsonaro and some of his allies had made unfounded claims about electoral fraud and unfair treatment by the press.
Some of his supporters are still waiting to hear from him; truck drivers blocked major arteries and highways in at least 12 Brazilian states on Monday, claiming that the race was too close and that they wanted to hear from Bolsonaro, according to CNN Brasil.
But public concession or not, experts say it's already out of the outgoing President's hands.
It is Brazil's Supreme Electoral Court that officially validates election results and communicates them to the Senate, Chamber of Deputies and State Assemblies.
A press officer for the Electoral Court told CNN that the vote's results are already considered validated, since the court's declaration of the outcome on Sunday. A court session at a later point will formally confirm the win, but no date has been set for it yet, he said.
Electoral Court President Alexandre de Moraes on Sunday personally called both Lula da Silva and Bolsonaro to inform them of the results and congratulate them on their participation in the democratic process, according to a press release by the Court.
De Moraes also said he did not see much room for the election to be contested. "The result has been proclaimed, accepted and those who were elected will take office on January 1," he said in the release.
Brazilian Senate President Rodrigo Pacheco has already publicly congratulated Lula da Silva and his supporters, as has Chamber of Deputies President Arthur Lira -- a close Bolsonaro ally.
Foreign leaders from across the globe have also expressed their support for Lula da Silva's win, swiftly issuing statements recognizing him as President-elect.
"I send my congratulations to Luiz Inácio Lula da Silva on his election to be the next president of Brazil following free, fair, and credible elections," US President Joe Biden said after Sunday's vote.
And Russian President Vladimir Putin sent congratulations in a message reported by Russian state news agency TASS, adding: "The vote's results confirm your high political authority."
The President-elect's diplomatic work is already underway, with Lula da Silva meeting Argentine President Alberto Fernandez -- one of the first foreign leaders to congratulate him -- in Sao Paulo on Monday.
Previous Refusals to Concede
At least twice before, Brazilian leaders have refused to participate in the transfer of power.
At the start of the Brazilian republic in the late 19th century, army marshall Floriano Peixoto did not attend the inauguration of his successor, Prudente de Moraes.
And almost a century later, the last of the unelected military presidents, João Batista Figueiredo, snubbed the inauguration of his successor José Sarney.
In both cases, the boycott was largely symbolic. The same would be true if Bolsonaro were to refuse to concede the presidency in a public statement, according to legal expert Augusto de Arruda Botelho.
"Not acknowledging the result is a non-starter from the political point of view, because at the end of the day, it is the Electoral Court that hands over power to the winner of the election," he told CNN.
"[Bolsonaro] can kick and scream as much as he wants," he added.
Plus it is in Bolsonaro's political interest to appear the good sport, political scientist Camila Rocha told CNN.
Rocha's research shows that refusing to concede would be damaging for Bolsonaro's public image among his own supporters. "Even the most extreme pro-Bolsonaro supporters, like those I interviewed last year in Santa Catarina for my research, say that if Bolsonaro lost he would have to accept the result," she told CNN.
"So it is very clear that if Bolsonaro refuses to accept Lula's victory, it could have a negative impact even among his supporters. He would certainly be perceived as a bad loser."
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