Patriotic symbols like Brazil's national flag and football shirt have long been co-opted as the uniform of Bolsonaro's right-wing base, but some also donned Trump paraphernalia.
Crowds demanded "Amnesty!" and "Moraes, out!"
Another protester, Erica, said the trial was "just a big theatre because everyone knows his conviction is already determined".
But there are many here who disagree.
At a nearby rally of Bolsonaro opponents, crowds chanted "no amnesty" and "dictatorship, never again".
Huge inflatable figurines of Bolsonaro in a prison uniform and Trump bobbed above signs saying: "Prison for Bolsonaro" and "Trump, paws off Brazil".
One wore the football shirt, which left-wing Brazilians hope to reclaim, saying "I'm not a Bolsonaro minion".
The crowd was optimistic he could be convicted.
One of the protesters, Rafael, called Bolsonaro's arrest a "victory", accusing him of having committed "serious crimes" against Brazilians.
"It's still very polarised. Until recently, the right was strong. But since Trump's actions there's been a shift to the left. It's about sovereignty and preventing foreign interference," he added.
"All the evidence shows it was a coup attempt," said Karina. "I hope justice is done to show you can't do whatever you want for your own gain."
This trial has carved deep rifts and reignited debates about democracy in Brazil.
The 8 January riots and the coup allegations are so troubling to Bolsonaro critics because Brazil's democracy is still young.
It was restored in 1985, after two decades of a dictatorship backed by the US.
The Supreme Court casts itself as guardian of this democracy.
But it has become a lightning rod. Its judges are appointed by presidents but can also put presidents and ministers on trial.
Some sit on the electoral court and strike down laws. Its president was once Lula's lawyer, adding fuel to accusations of bias from Bolsonaro supporters.
An inquiry into fake news, including online threats to the court, led by Justice Moraes has jailed Bolsonaro allies and taken down social media accounts.
Critics say this stretches the court's remit into policing and politics; supporters call it a model for the digital age.
The court's role in Bolsonaro's trial, in which Moraes is both a rapporteur and the target of the alleged assassination plot which is part of the case, has led both sides to accuse the other of authoritarianism.
Bolsonaro's critics argue he attempted to install a dictatorship.
His supporters, on the other hand, say the sweeping powers the court has used to investigate the alleged coup and the rioting in the capital, Brasília, are an abuse of judicial powers.
Those who believe the judiciary has gone too far in prosecuting people involved in the storming of government buildings on 8 January 2023 often cite the case of Débora Rodrigues dos Santos.
The 39-year-old Bolsonaro supporter received a 14-year sentence after scrawling "You lost, idiot" in lipstick on the statue of Justice outside the Supreme Court.
Claudia credits Bolsonaro's "love for the flag" with inspiring "housewives, the WhatsApp aunt, the bricklayer, the businessman" to engage in politics.
She argues that, because no coup materialised, Bolsonaro cannot be guilty of one.
"If he is convicted of a coup, that also condemns 1,200 people who were protesting there," she said.
But there are others who think the events of 8 January 2023 were much more than a simple protest.
Ricardo Cappelli is the former minister tasked with restoring order in Brasília after the storming of the key buildings.