Brazil's President Jair Bolsonaro is calling supporters to attend street rallies alongside Independence Day military parades on Wednesday, a showing that may gauge support for the far-right leader's attacks on democratic institutions ahead of an October election.

In the capital Brasilia, security officials are bracing for a crowd of 500,000 people on the central mall, which Bolsonaro will address after overseeing the traditional military parade marking 200 years of Brazil's independence from Portugal.

Police have reinforced security along the grassy esplanade to prevent any efforts to advance on the Supreme Court, where they threatened to march a year ago in a demonstration inspired by the Jan. 6, 2021 assault on the U.S. Capitol.

Bolsonaro's attacks against Brazil's voting system - and the courts that run it - have stirred calls for a military coup from his radical backers. Some fear he is laying the groundwork to claim electoral fraud like his U.S. ally, former President Donald Trump, and reject any victory by leftist rival Luiz Inacio Lula da Silva, which polls show leading the race ahead of an Oct. 2 vote.

Bolsonaro has claimed the polls are skewed, the courts favor Lula and that Brazil's electronic voting is rife with fraud, without providing proof. When pressed on national TV two weeks ago, he said he would respect the election result as long as voting is "clean and transparent," without defining any criteria.

Bolsonaro's rhetoric on election integrity and the electoral courts will come under close scrutiny on Wednesday, along with his efforts to blur the lines between military celebrations and his own presidential campaign.

Bolsonaro, a former army captain who has told supporters the army is "on our side," pushed to transform a traditional Independence Day military display in Rio de Janeiro into a second political rally on Wednesday afternoon.

Army brass balked at an initial proposal to march troops and tanks along the famous Copacabana Beach, but have reached a compromise with the commander-in-chief. Bolsonaro will accompany symbolic cannon fire, paratrooper displays, air force acrobatics and a naval parade before addressing a political rally there.

The rallies in Rio and Brasilia will fire up Bolsonaro's core supporters, but he runs the risk of boosting high rejection numbers if his rhetoric runs hot, as it did on Independence Day last year. At the time, he insulted Supreme Court Justice Alexandre Moraes and threatened to disobey his rulings - comments he soon walked back under intense political pressure.

Moraes, now in charge of Brazil's top electoral court, has not flinched in his showdowns with Bolsonaro and his backers. Last month he authorized police raids of businessmen supporting the president after a media report accused them of discussing a coup if he loses in October.

Bolsonaro's campaign managers have advised him to avoid attacks on the judiciary, but they could not rule out a repeat of last year.

"No one can hold Bolsonaro back. His core supporters are infuriated now by Moraes and will show it on Sept. 7," said a source in the president's campaign who was not authorized to speak freely.