"Good morning, President Lula!" This is what activists camping out in front of the police headquarters in the Brazilian city of Curitiba have shouted each morning for a week, hoping the country's ex-President Luiz Inacio Lula da Silva hears it. On Saturday evening, Lula started serving his prison sentence in Curitiba for corruption and money laundering. And supporters from his Workers' Party (PT) vowed to stay put until Lula is released.

Read more: Workers Party keeps Lula presidential bid alive

This could take quite a while. The initial optimism of Lula's lawyers has vanished. They were convinced that the Supreme Court of Brazil (STF) would not uphold the 2016 court decision on his prison sentence. They had hoped he could stay free until he had exhausted all his appeals.

Lula wants to run in the upcoming presidential elections in October. But supporters of "Operation Car Wash," a wide-ranging investigation into corruption in the country, have now come to dominate Brazil's top court.

This is bad news for the politicians tied up in the corruption scandal involving Lula. On Thursday, the STF decided not to temporarily suspend former minister Antonio Palocci's detention. Palocci has been in pre-trial detention for one and a half years.   

Next week, the STF will decide whether or not to charge senator Aecio Neves from the Brazilian Social Democracy Party (PSDB).

The court now seems to be assuming a kind of vanguard role, heralding in a new era in which corrupt politicians actually come to face justice. Previously, STF judges had seemed rather lenient towards PSDB politicians. Now, after Lula's arrest, Brazil's judiciary has to show it is taking a tough stance with PSDB members.

Read more: Who is Brazil's ex-president Lula?

'Operation Car Wash' for everyone

However, the public was surprised when the country's judiciary handed over the investigations against PSDB front-runner, Geraldo Alckmin, to the Superior Electoral Court (TSE): He is alleged to have accepted illegal campaign funding. The TSE is generally considered a toothless tiger, but this meant that Alckmin was spared being investigated as part of the feared "Operation Car Wash."  

This sparked an outcry on social media. Lula's PT party complained of double standards, arguing that the former president was being subjected to full force of the law, whereas Alckmin was being treated favorably. This fierce reaction could well force the judiciary to change its stance and hand over Alckmin's case to be dealt with by "Operation Car Wash" after all, since the judiciary's credibility is on the line.

Lula's PT party, meanwhile, can only resort to showing solidarity with the former president. Party members in Congress want to adopt the additional first name "Lula" so that the former president's name appears on the attendance records in parliament. But this gesture, along with last week's referral of the case to the UN Human Rights Council in Geneva, can do little to help Lula. Thus far, Brazilian governments have consistently ignored UN decisions.

It is slowly dawning on the PT that Lula will be remaining in jail. And that he will not be able to run for president in October, due to a law prohibiting convicted politicians from doing so. Now, calls for an alternative candidate are getting louder inside the party. And this alternative would probably be Sao Paulo's former mayor, Fernando Haddad. 

Yet for now, the PT leadership is still officially sticking with Lula. The concern is that deposing him as their candidate would send a fatal signal to their own party.

Barbosa to benefit

Things are also getting serious for incumbent president Michel Temer. He is facing another charge by the Attorney General's office. Earlier this week, two of his closest associates found themselves in the dock. It is alleged that they accepted bribes on his behalf. Last year, Temer had two charges blocked by Congress.

But he has now used up the political capital he once enjoyed. Now, with six months to go until the elections, members of Congress will hardly save "toxic" Temer once more from the judiciary. House Speaker Rodrigo Maia has long since stopped backing the president. He hopes to conquer Brazil's political center as Temer's center-right party MDB loses influence.

So far, Temer insists he will run for a new term as president. But there are indications that Finance Minister Henrique Meirelles will be most likely named as the MDB's candidate instead. Yet opinion polls show that both are hopelessly behind.

Far-right politician Jair Bolsonaro's odds, however, look much better. As do those of Brazil's former environmental minister, Marina Silva. The two outsiders are benefiting from the existential crisis that the country's major parties currently find themselves in. But they will have difficulty explaining to their voters how they intend to govern without the support of Brazil's major Congress parties.

The country's former chief justice Joaquim Barbosa, who several days ago surprisingly joined the Brazilian Socialist Party (PSB), seems to have a better shot at winning. Barbosa is not a career politician and has a reputation as Mister Clean, and for being a hardliner. His outstanding role in the "Mensalao trial" that dealt with leading figures in the infamous vote-buying scandal earned him a Batman-like image. In 2016, he spoke out against impeaching Dilma Rousseff. Barbosa would likely have the backing of Brazil's left-wing parties should Lula not run for presidency. And Barbosa certainly has what it takes to pull off a surprise victory in the October elections.