The election was marred by technical glitches, including a stalled vote count.
Duterte-backed candidates were poised to take nine of the 12 senate seats available, with just one seat possibly going to the opposition. Independents were due to win around two seats.
A senate majority lessens the chance of censure and lower house probes against the 74-year-old Duterte and make it easier to pass his legislation, such as restoring capital punishment, reforming the tax system, changing the constitution to introduce federalism and a possible extension of the strongman’s term limits.
Duterte has also pledged to lower the age of criminal responsibility from 15 to 12.
The upper house has been a bulwark against some of Duterte’s most controversial proposals.
Traditionally, the 24 senators, who serve six-year terms, have been more independent-minded than lower house representatives.
The new senators include his former aide Bong Go and Ronald dela Rosa, the police chief who oversaw Duterte’s so-called war on drugs. Senator Bam Aquino, the only opposition candidate with a chance, dropped to 14th place.
Monday’s ballot for more than 18,000 posts, among them hundreds of mayors, governors and congress representatives, was billed as a referendum on Duterte, with the focus on his upper house bid.
Duterte triumphed despite international criticism for his anti-drug campaign that has left thousands dead and for his increasing pursuit of critics, including the independent journalist Maria Ressa.
Duterte’s extrajudicial drugs killings are central to his populist appeal that has buoyed his remarkable popularity among Filipinos since taking office in 2016.
The Philippines outlawed capital punishment in 1987 after the fall of dictator Fidel Marcos, reinstated it six years later and then re-abolished it in 2006.
Duterte has promised to create a federal republic where regions would be given the power to address deep-rooted poverty.
However, the opposition sees federalisation as an effort to extend Duterte’s grip on power or weaken the nation’s democratic institutions.
“I voted for many of the candidates endorsed by President Duterte because his government is doing its job,” said 51-year-old Myrna Cruz in Manila.
“I support their programmes, including the anti-drug campaign … but I wish the bloodshed would stop,” she said in an apparently contradictory statement.
“This president’s popularity and transferability of his popularity is unprecedented to say the least, despite all the controversies,” analyst Edmund Tayao told Reuters. “You expect normally two or three candidates from the opposition to win but this is a wipe-out.”
More than 5,000 Filipinos have been murdered since 2016. Picture credit: Wikimedia