Voters choosing Mexico’s next president are deciding Sunday between a former academic who promises to further the current leader’s populist policies and an ex-senator and tech entrepreneur who pledges to up the fight against deadly drug cartels.

In an election likely to give Mexico its first woman president, nearly 100 million people are registered to vote in the race to replace outgoing President López Obrador. Voters will also elect governors in nine of the country’s 32 states, and choose candidates for both houses of Congress, thousands of mayorships and other local posts.

The elections are widely seen as a referendum on Mr. López Obrador, a populist who has expanded social programs but largely failed to reduce cartel violence in Mexico. His Morena party currently holds 23 of the 32 governorships and a simple majority of seats in both houses of Congress. Mexico’s constitution prohibits the president’s reelection.

Ms. Morena hopes to gain the two-thirds majority in Congress required to amend the constitution to eliminate oversight agencies that she says are unwieldy and wasteful. The opposition, running in a loose coalition, argues that would endanger Mexico’s democratic institutions.

Both major presidential candidates are women, and either would be Mexico’s first female president. A third candidate from a smaller party, Jorge Álvarez Máynez, trails far behind.

Mexico City’s mayor, Claudia Sheinbaum, is running with the Morena party. Ms. Sheinbaum, who leads in the race, has promised to continue all of López Obrador’s policies, including a universal pension for the elderly and a program that pays youths to apprentice.

Opposition presidential candidate Xóchitl Gálvez, whose father was Indigenous Otomi, rose from selling snacks on the street in her poor hometown to start her own tech firms. A candidate running with a coalition of major opposition parties, she left the Senate last year to focus her ire on Mr. López Obrador’s decision to avoid confronting the drug cartels through his “hugs not bullets” policy. She has pledged to more aggressively go after criminals.

The persistent cartel violence, along with Mexico’s middling economic performance, are the main issues on voters’ minds.

The Mexican peso has strengthened against the dollar in recent years, mainly because of high domestic interest rates and a huge surge in money sent home by migrants. But the gross domestic product has averaged only about one percent growth per year under the current president.

Mr. López Obrador claims to have reduced historically high homicide levels by 20 percent since he took office in December 2018. But that’s largely a claim based on a questionable reading of statistics; the real homicide rate appears to have declined by only about 4 percent in six years.

About 675,000 Mexicans living abroad are registered to vote, but in the past only a small percentage have done so. Voting is not mandatory in Mexico, and overall turnout has hovered around 60 percent in recent elections. In the Trump-Biden matchup in 2020, American voter turnout was 67 percent, its highest point in decades.

Just as the upcoming November rematch has underscored deep divisions in the United States, Sunday’s election has revealed how severely polarized public opinion is in Mexico over the direction of the country, including its security strategy and how to grow the economy.

Beyond the fight for control of Congress, the race for Mexico City — whose top post is now considered equivalent to a governorship — is also important. Ms. Sheinbaum is just the latest of many Mexico City mayors, including Mr. López Obrador, who went on to run for president. Governorships in large, populous states such as Veracruz and Jalisco are also drawing interest.

Polls open at 8 a.m. and close at 6 p.m. in most of the country. The first preliminary, partial results are expected by 9 p.m., after the last polls in different time zones close.