Adding to the rancor are a long-simmering dispute over discretionary funds and disagreements over political agendas.
The tensions demonstrate how political alliances in the Philippines tend to be short-lived, often struck simply for politicians to consolidate support ahead of elections. Political dynasties, with all their money, influence and grassroots support, hold power in shaping who becomes president.
The discord began with President Ferdinand Marcos Jr.'s administration slashing Vice President Sara Duterte's confidential budget. This followed media reports last year detailing her spending of roughly $2.2 million in just 11 days early in her term.
The confidential funds -- lump sums that can be spent by government agencies without official oversight -- were the focus of a parliamentary investigation in late 2023, with Congress demanding explanation of their use. House Speaker Martin Romualdez, a close ally and cousin of Marcos, denied initiating the investigation for political purposes.
Tensions escalated when Duterte's confidential funds were completely cut from her office's 2024 budget while Marcos' own discretionary funds remained untouched. Nonetheless, Duterte publicly reaffirmed her support for the Marcos administration.
Analysts say the discord runs deeper than budget issues. Anthony Lawrence Borja, an assistant professor at De La Salle University in Manila, noted that the funds were just one of "the first breaking points" of the dynastic alliance.
"Oligarchs think that public funds are basically private funds. So they're trying to split the booty," he told Nikkei Asia.
Cleve Arguelles, a political scientist and the CEO of the Manila-based public opinion research company WR Numero, said the split was inevitable given the "uncomfortable alliance" between the dynasties to begin with.
"Remember, if you backtrack a bit, prior to the announcement that 'Uniteam' had been formed, the former president (Rodrigo Duterte) didn't want [Sara, his daughter] to run with 'Bongbong,'" he told Nikkei Asia, referring to Marcos by his nickname.
"You can also remember that during this time, there was also an attempt by the father to portray Bongbong as a weak leader," Arguelles added.
The Marcoses' return to power was aided in part by the Dutertes as the two dynasties built an alliance in the run-up to the 2022 presidential election. The incumbent president is the son of ousted dictator Ferdinand Marcos, who ruled from 1965 to 1986 and instituted martial rule that weakened the economy and public institutions.
The Dutertes amassed power in Davao, their bailiwick in the south, by ruling the city with an iron fist for two decades.
The recent animosity spilled over to the Duterte family, with former President Duterte's eldest son, Paolo, facing scrutiny for extravagant public spending. On Jan. 28, tensions erupted at separate rallies. The Dutertes held a gathering in Davao opposing the "people's initiative" movement to amend the constitution, though ironically Rodrigo Duterte had pushed for federalism during his own presidency.
Meanwhile, the Marcos administration launched its Bagong Pilipinas (New Philippines) campaign, highlighting a growing divergence between the two dynasties. The event was a revival of sorts of his father's political movement, Bagong Lipunan (New Society).
At the Davao event, Rodrigo Duterte launched a tirade against the incumbent president, calling him a "drug addict." His youngest son, Sebastian Duterte, the current mayor of Davao, even demanded Marcos' resignation.
The country's drug enforcement agency said Marcos was never on the government's "drug watchlist."
Marcos responded by suggesting that Rodrigo Duterte's accusations stemmed from his use of fentanyl for pain management.
"I think it's the fentanyl. Fentanyl is the strongest painkiller you can buy. It is highly addictive and has very serious side effects," he said, accusing Duterte of "taking the drug for a very long time now."
Duterte admitted to using fentanyl as a painkiller after being injured in a motorcycle accident in 2016 but said he ceased use before becoming president.
De La Salle University's Borja said that despite the animosity now, political loyalties could still shift in the lead-up to the 2025 midterm elections.
Those elections are crucial for Marcos to fill Congress with his party's lawmakers to ensure the passage of policies he favors. Former President Duterte snagged a supermajority of lawmakers in the 2019 midterm polls, effectively crippling his political opposition.
"There is a chance for the Duterte-Marcos unity to be reasserted," Borja said, "or it can be a giant split between at least three camps: the old liberal opposition ... Duterte consolidating [a] position as opposition and the Marcos camp."
On the other hand, Arguelles noted that the president and vice president need to maintain an appearance of unity for now. Duterte bombarded the news cycle in recent days, reaffirming her support for the Marcos administration and denying that she had masterminded death squads in Davao, the subject of a looming investigation by the International Criminal Court at The Hague.
"If they divide themselves into two different camps, it's easier to conquer them because it's just plurality -- they will no longer have this supermajority," Arguelles said.
Additional reporting by Ella Hermonio