Activists in favor of the legalization of abortion comfort one another Thursday outside the National Congress in Buenos Aires after senators rejected the bill to legalize abortion. (Eitan Abramovich/AFP/Getty Images)

After months of debates and a close favorable vote by the Argentine House in June, the Argentine Senate has voted down a bill that would have legalized abortion. Despite House support and a large feminist mobilization on behalf of the bill, the Senate — which over-represents the votes of rural and conservative constituencies — rejected the bill, 38 to 31.

Here are five things to know about the politics of legalizing abortion in Argentina.

1. The law would have been a big advance for proponents of legalized abortion in Latin America

This project proposed to change Argentina’s criminal code, under which abortion is illegal except when the life of the mother is endangered, or if the pregnancy comes from a rape or an attack committed on a mentally impaired woman. The bill would have decriminalized abortion up to 14 weeks of pregnancy, provided free abortion in public and private hospitals, mandated a waiting period of five days to secure an abortion, and required counseling and medical treatment before and after the procedure.

In Latin America, only Cuba, Uruguay and Mexico City have legalized abortion before the 12th week of pregnancy. Numerous Latin American countries have liberalized their abortion laws since 2000 by expanding the circumstances when abortion is not punishable. Nevertheless, a majority of the 19 countries in the region still ban abortions or allow them only when the mother’s life is at risk. These numbers are not surprising in a region that concentrates the greatest proportion of Catholics in the world.

2. A women’s right movement has been growing in Argentina

So how could an abortion bill get even this far in Argentina? It’s because of a new movement called #NiUnaMenos (Not one [woman] less). In May 2015, a pregnant 14-year-old, Chiara Paez, was found beaten to death and buried under her boyfriend’s house; the boyfriend soon confessed. That femicide triggered a massive mobilization against violence against women, with nearly 200,000 Argentines protesting in front of Congress that June and thousands more mobilizing across the country.

The movement soon expanded its agenda to a broader defense of women’s rights, becoming important in Argentine politics. Mobilizations after new cases of violence against women spread through Latin America, signaling regional resistance against gender-based violence.

3. The pro-abortion coalition piggybacked on the broader women’s rights movement

The pro-abortion bill promoters strategically linked their demands to #NiUnaMenos’s broader social movement on behalf of women’s rights. They did so by framing the debate as being about violence against women, arguing that denying the right of abortion equaled risking women’s lives, thus identifying every woman seeking an abortion as a victim. The coalition used a green scarf as the icon for their demonstrations; the scarf had for years been the badge of La Campaña, the foundational network of pro-abortion organizations.

La Campaña had pushed Congress to legalize abortion for about a decade. Juliana Di Tullio, House majority leader during the last two years of then-President Cristina Kirchner’s administration, wrote bluntly in a recent op-ed that the fear of losing a floor vote in Congress was always stronger than the hope of passing a bill. Pro-abortion forces had held back from demanding a congressional debate, lest they be defeated.

4. Popular pressure worked, up to a point

This year was different. Women were actively mobilizing for feminist goals, with frequent spontaneous protests. When #NiUnaMenos planned a protest in front of Congress for International Women’s Day this past March, legalizing abortion topped their demands. Acknowledging this popular pressure, President Mauricio Macri, the leader of the conservative party PRO, argued in his opening speech that Congress should debate abortion rights.

Advocates of abortion rights in the House, where women legislators have been especially vocal, exploited this rare opening and brought the issue — taboo for decades — to a vote. As even some members of conservative parties supported the bill, the House voted narrowly in favor. Conservative supporters leaned on the president’s speech and #NiUnaMenos’s framing of abortion as an anti-violence measure to justify their support and shield them from sanction by their party.

The result? A narrow House victory in favor of abortion rights this past June.

5. Malapportionment fueled a conservative backlash in the Senate

The debate took conservative elites and the Catholic Church by surprise. Many did not expect the issue would be brought to the floor in a period of conservative control. The countercampaign, #SalvemosLasDosVidas (or Save the Two Lives), did not gear up until after the House vote. Conservatives framed the debate in black and white, rejecting any change to the current law. What’s more, opponents offered no alternative proposals; potential amendments came instead from moderate senators.

So how was the abortion bill blocked? By the institutional design of the Argentine Congress. By one prominent measure, the Argentine Senate is the most malapportioned chamber in the world. Most of its population is concentrated in three provinces, out of a total of 24. But each of those 24 provinces elect the same number of senators.

In the case of the abortion bill, the most overrepresented provinces — meaning that senators from these regions represent fewer citizens, each of whose votes therefore has more power than the votes in highly populous provinces — had the highest concentration of abortion opponents. Argentine surveys found that the issue polarized voters. While the nation was split roughly 50-50, the two sides were concentrated in different regions. Specifically, more than half of the Senate represents the 13 provinces that form the Northeastern, Northwestern and Cuyo regions, which contain a bit over 25 percent of the country’s population. And fewer than a third of those regions’ voters supported the bill. The final Senate vote of 38 to 31 reflected that malapportioned divide.

Political scientist Samuel Huntington noted in 1968 that there’s a tension between modernization and institutions. A less-than-representative institutional design blocked Argentina’s abortion reform. Nevertheless, feminism’s momentum in the country is far from over. Promoters of the bill have already announced that they are committed to presenting a new proposal next legislative year.

Julia María Rubio is a PhD candidate in political science at Columbia University.