Colombia’s presidential campaigns are both flagging the risk of fraud in Sunday’s election, and taking steps to prevent it.

Conservative frontrunner Abelardo de la Espriella is working with Venezuelan opposition leader María Corina Machado. Her movement built a sophisticated election-monitoring organization, battle-hardened by decades of dirty tricks from the regime in Caracas.

Meanwhile, his leftist rival Iván Cepeda, is relying on a grassroots network of young volunteers.

Both teams are seeking to have eyes in as many polling stations as possible on June 21.

With fewer than 700,000 ballots separating De la Espriella and Cepeda in the first round, in a country of more than 40 million eligible voters, both campaigns are anxious to eke out any advantage they can.

A lot is at stake. If Cepeda wins, Colombia’s left will have another four years to continue its overhaul of the nation’s economic model, oil industry and welfare system. With a victory for De la Espriella, Colombia would become another South American government aligned with U.S. President Donald Trump, alongside Argentina, Ecuador, Bolivia and Chile.

Fraud claims

Unlike electoral observers, who typically visit multiple polling stations, vote witnesses remain assigned to a single table from the opening of polls through the preliminary count and subsequent scrutiny. They monitor compliance with electoral procedures, and document and report any irregularities.

Parties participating in the first round had enough witnesses to cover more than 98% of the roughly 120,000 voting tables nationwide, according to the National Electoral Council.

Each campaign is allowed to appoint one witness per table. Authorities also accredited nearly 14,000 domestic observers and 1,300 international observers.

De la Espriella outperformed most poll forecasts to finish first in the May 31 vote with 44% of ballots cast, compared to Cepeda’s 41%. Within hours of the preliminary count, Cepeda’s ally President Gustavo Petro said he did not recognize the results, alleging irregularities in the electoral software and voter registry. Cepeda initially echoed some of those concerns, then said that the count had been fair.

De la Espriella responded by calling for expanded international scrutiny of the runoff and urging allies in the U.S. and elsewhere to support election-monitoring efforts.

Electoral authorities later rejected allegations of irregularities in either the preliminary count or the scrutiny process, a conclusion echoed by international observer missions, including the European Union’s.

Allegations of irregularities in Colombian elections have tended to center on practices such as vote buying or coercion, while the system in place to count ballots is “very robust”, former head of the electoral authority Juan Carlos Galindo said in a phone interview.

Machado’s team

For Machado, the Colombian runoff represents the latest test of a model that helped Venezuela’s opposition challenge Nicolás Maduro’s claim of victory in 2024. Her movement trained tens of thousands of volunteers to monitor voting tables, collect official tally sheets and rapidly transmit results to a centralized database.

Advisers from her movement also supported monitoring efforts last year in Honduras, Ecuador and Bolivia.

Machado also discussed election-monitoring cooperation with Democratic Center candidate Paloma Valencia, according to people familiar with the talks. Valencia failed to make it to the runoff, and endorsed De la Espriella.

Machado’s team identified “unusual voting patterns” in several Colombian regions during the first round, said her electoral adviser Humberto Villalobos. Those findings helped De la Espriella’s campaign identify high-risk and high-turnout voting centers on which to concentrate oversight efforts in the runoff, Villalobos said.

Cepeda’s campaign, meanwhile, is recruiting witnesses through WhatsApp groups organized by city and neighborhood supporters.

“You don’t need to be a lawyer, you don’t need experience,” one recruitment message reads. “It’s about being there, protecting the vote and ensuring the will of the people is respected.”

The campaign tapped a range of groups, including university students, feminists, farmers and environmentalists, and even from among K-pop, Justin Bieber and Taylor Swift fan clubs.

Polls are open from 8 a.m. to 4 p.m. on June 21. Results expected later that evening, while the official scrutiny process will continue in the following days.

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