Former President Rodrigo Duterte accused Marcos last month of using drugs and publicly floated the idea of a military coup to unseat the president. Last week, he proposed the secession of Mindanao, a southern island and the base of his political power.

Marcos initially responded by saying his predecessor’s judgement had been impaired by his use of the synthetic opioid fentanyl, which he previously admitted to using to recover from a motorcycle accident. He also said the call for a separate Mindanao was “doomed to fail”, and his national security adviser threatened to use force to quell any secession attempts.

The ongoing political spat has put Duterte-Carpio in a bind, threatening to unravel the alliance crafted by her and Marcos before they were elected in 2022.

She has recently split with the president on several issues, including the government reopening peace talks with communist rebels and an ongoing investigation of her father’s deadly drug war by the International Criminal Court.

But the Marcos administration’s effort to change the Philippine constitution has created the biggest cleavage between the country’s two most prominent political families.

Marcos says he wants to remove existing constitutional restrictions that limit foreign investment. Critics in the Duterte political camp, however, accuse Marcos of plotting to switch the country to a parliamentary system and install House Speaker Martin Romualdez, Marcos’s cousin and a close ally, as his successor before the next presidential election in 2028.

Duterte-Carpio has tried to remain neutral, even as her father’s attacks on the president have continued. She was the only member of the Duterte family to appear with Marcos last week when the president visited flood-hit areas of Mindanao.

“She wants to keep the Marcos-Duterte alliance together,” said Walden Bello, an adjunct professor of sociology at the State University of New York at Binghamton and former member of the Philippine House of Representatives. “That sort of political arithmetic was the key in 2022, and that’s going to be key in 2028.”

‘Not just her father’s daughter’

The Marcos-Duterte alliance was formed after Duterte-Carpio shocked the country by opting not to run for president in 2022, even though she was the odds-on favourite.

Instead, she defied her father’s wishes and opted to run for vice president and support Marcos’s presidential bid – in the Philippines, the president and vice president are elected separately.

Her decision all but ensured the pair would win and prevented an upset victory by opposition candidate Leni Robredo, the former vice president and a vociferous critic of Duterte’s drug war.

“It was a perfect marriage for the 2022 election,” said Cleve Arguelles, chief executive of the polling firm WR Numero Research.

It was also an early sign of Duterte-Carpio’s autonomy from her father, whom she succeeded as mayor of Davao, the largest city in Mindanao. During her time as mayor, she replaced staffers loyal to her father and forged her own set of alliances, including a bond with Imee Marcos, the current president’s sister. The two remain politically aligned.

“She’s not just her father’s daughter,” Arguelles said.

Duterte-Carpio also cuts a figure different from many of the country’s past prominent female politicians, who have often cast themselves as maternal figures. As Davao mayor, she made headlines for punching a court sheriff. She often wears military fatigues and has joked about cutting her hair short when she wants to appear tough.

After their election win, Duterte-Carpio publicly said she wanted to be named defence secretary – in the Philippines, it is common for the vice president to also take a cabinet position – but Marcos named her education secretary, which was widely seen as a snub.

“That was a very quick lesson that, oh, you’re not president,” Arguelles said. “There’s no such thing as sharing presidential powers.”

Last year, Duterte-Carpio was heavily criticised for requesting about $11.6m in “confidential funds”, which would be used without oversight, in the 2024 national budget.

The controversy pulled down her public approval rating from 84 percent in June 2023 to 73 percent in September – still higher than that of Marcos, who registered 65 percent approval. It also created a perception that Marcos’s allies, especially Speaker Romualdez, were plotting against her.

“She’s kind of stuck in this alliance,” Arguelles said. “She can’t totally abandon the administration because she knows it’s going to be fatal.”

‘Double game’

Duterte-Carpio’s father and her younger brother, current Davao Mayor Sebastian Duterte, have continued to pressure the president during speeches in Mindanao – and the country’s economic realities could help their cause.

Inflation fell to 2.8 percent in January, down from 3.9 percent in December. Rice inflation, however, hit its highest level since 2009, reaching 22.6 percent and threatening a Marcos campaign promise to stabilise prices of the staple food.

The Dutertes “are going to really play that up”, Bello said, using furore over rice prices to give energy to their opposition to changing the constitution, which many presidents – including Duterte – have tried unsuccessfully since it was ratified in 1987.

Marcos insists his motivations are economic in nature, aimed at removing limits on foreign ownership in companies operating in the Philippines. But that has not quelled speculation that it is a ploy to block a Duterte-Carpio campaign by switching to a parliamentary system, under which elected representatives would build a coalition and choose a prime minister.

“There’s [already] a great deal of foreign investment coming in,” Bello said. While companies have learned to work around the current restrictions, “it’s the corruption and instability that worries them”.

“And [constitutional change] is going to create such instability at this point in time,” he said. “It’s really roiled the political scene and focused people on the fight between the Marcoses and Dutertes.”

Duterte-Carpio has been cautious in expressing her own opposition to constitutional change, directing her public ire at Romualdez rather than Marcos. In past weeks, both Marcos and Duterte-Carpio have insisted they remain on good terms.

But political manoeuvring by the Marcos camp pressures Duterte-Carpio, who is not a natural politician, said Tony La Vina, associate director of climate policy and international relations for Manila Observatory.

“Everything is black and white for [Duterte-Carpio], from what we’ve seen,” he said. “She doesn’t have any patience for discourse.”

The Dutertes are also growing worried about the ongoing ICC drug war investigation.

The Hague-based court could issue a warrant of arrest for Duterte in the coming months – and while Marcos has said the Philippines would not cooperate with the ICC, he also said its investigators may enter the country on their own terms.

Duterte-Carpio “did not seek an early split, but I think that things ran out of control”, Bello said. “She’s going to try until the end to play this double game”.

It has had the effect of eroding the opposition and turning Philippine voters into an “audience” for a family feud, Bello said. “It’s the politics of spectacle that’s going to reign over the next few years.”