Supporters of former Brazilian president Luiz Inacio Lula da Silva attend a rally in Curitiba, Brazil, on Aug. 30. The sign reads “Free Lula.” (Reuters)

The Brazilian Superior Electoral Tribunal (TSE) last week barred Brazil’s most popular politician — former president Luiz Inácio Lula da Silva, known as “Lula” — from running for president in this fall’s national elections.

Why? Because Lula is in jail, serving a 12-year sentence for corruption. Granted, the electoral tribunal’s decision could still be appealed. But the decision shakes up Brazil’s already unstable political situation. As a result, an authoritarian, outsider candidate who has promised to return Brazil to military rule may end up winning.

Here are six things to know about the upcoming elections.

1. Lula’s party could appeal the court’s decision

If Lula appeals the electoral tribunal’s ruling, the case would land in the hands of Brazil’s Supreme Court, which must announce its decision on his candidacy by Sept. 17.

The election will take place Oct. 7. Under Brazil’s electoral system, if no candidate achieves a majority, the top two vote-getters advance to a runoff, to be held Oct. 28. Traditionally, voters coalesce around a candidate from a major party in the second round. But with 13 candidates on the first round ballot, the vote may be split among so many competitors Brazilians might have to choose between two nontraditional contenders in the runoff.

2. There’s a bigger political crisis in Brazil beyond who’s on the ballot

Brazil is a country in turmoil. It is just beginning to emerge from its worst recession in history. The economy contracted by 8 percent, the unemployment rate is 13 percent, and crime and violence are at all-time highs, with over 60,000 homicides reported last year in a country of 210 million.

Moreover, the government has been embroiled in corruption scandals since 2014. Not only is Lula in jail, but the Brazilian Congress impeached his successor, Dilma Rousseff, and the current president, Michel Temer, has been indicted.

Even in prison, Lula remains extremely popular. Born in poverty, Lula became a labor activist who opposed the military dictatorship in the 1980s. After two terms as president, he left office with an approval rating over 80 percent. He is the only presidential candidate with widespread support and leads by a large margin in polls in which he is included.

3. The public has lost faith in the major parties

The corruption scandals have left Brazilian voters disillusioned with their traditional parties. The 2017 Latinobarómetro public opinion survey found that 72 percent of Brazilian respondents had “no confidence at all” in political parties while 19 percent had “little confidence.” Temer’s approval rating is in the single digits. His handpicked candidate for president for his Brazilian Democratic Movement party, former finance minister Henrique Meirelles, polls at roughly 1 percent, and more than a half-dozen other mainstream candidates have less than 10 percent support as well.

Fernando Haddad, running in place of Lula for the Workers’ Party (PT), has little popular support and faces corruption accusations himself. Polling suggests that if Lula isn’t on the ballot, 30 percent of his supporters will defect to other candidates while 40 percent will cast a blank ballot. Brazilians consistently cite corruption as the most important problem in the country, and parties across the board have changed their names to escape public exasperation with the existing party system.

4. A nontraditional candidate could step into the vacuum

As a result, many voters perceive outsiders as untainted. On the left, environmentalist Marina Silva is running for her recently created Sustainability Network party (REDE); some polls show her with double-digit support.

More significantly, voters are turning toward far-right candidates. Why? Many Brazilians are ambivalent about democracy: Half are open to some form of authoritarian rule. Brazil’s military regime (1964-1985) was comparatively less repressive than those of its neighbors. During that time, GDP averaged an annual growth rate of 6.2 percent. Many voters are now nostalgic for days when the streets were safer. Public confidence in the military is strong, generals have been talking openly about military intervention, and at least 90 candidates linked to the armed forces are running for public office in the upcoming elections.

Among those is presidential candidate Jair Bolsonaro of the Social Liberal Party, a former army captain who has openly promised a return to military rule if elected. Likened to President Trump, Bolsonaro has been criticized for disparaging comments against women, the LGBT community, ethnic minorities and foreigners. As a leader of a political coalition that joins the security forces, agribusiness and evangelicals — the so-called bullet, beef and Bible caucus — Bolsonaro may benefit from the traditional parties’ collapse and Lula’s loss at the tribunal.

5. Crumbling parties have propelled Latin American authoritarians

In Venezuela, when Hugo Chávez ran for the presidency in 1998, his initial support came from those who were ambivalent or even hostile toward democracy. But democratic voters propelled him to victory. The traditional parties, Democratic Action and the Christian Democrats, that had ruled since 1958 collapsed after economic crises. Personality rather than party swayed the presidential race.

This scenario has been repeated across Latin America. A cross-national study of those who held government positions during military rule and ran for office in the post-military rule era shows that traditional parties are crucial to democratic governance. Where long-standing, major parties competed in elections after military rule, they won most of the vote, soundly defeating ex-authoritarian candidates. Where such parties did not exist, or where the military regime’s parties became the major electoral vehicles after democracy returned, ex-authoritarians have been much more successful.

6. Expect chaos in October

Weak parties, a shaky economy, and rising crime and violence in Brazil mean that it’s hardly surprising that nontraditional politicians on the left and right are doing well so far. In head-to-head matchups with other candidates, for example, Bolsonaro outpolls each of his potential rivals. With Lula off the ballot, expect more turmoil from Brazil’s already chaotic political environment.

Brett J. Kyle is assistant professor of political science at the University of Nebraska-Omaha, where he is a member of the Office of Latino/Latin American Studies (OLLAS) and the Goldstein Center for Human Rights. He is the author of “Recycling Dictators in Latin America: Legacies of Military Rule” (Lynne Rienner Books, 2016).

Andrew G. Reiter is associate professor of politics and international relations at Mount Holyoke College. He has published widely on issues related to transitional justice, political violence, and military politics.