MANILA - President Rodrigo Duterte looked set on Tuesday to strengthen his grip on power after unofficial results of a mid-term election showed big wins for his candidates, and resounding public endorsement of his controversial rule.

Nine of 12 available seats in the all-important Senate looked set to go to pro-Duterte candidates and the rest to independents, unofficial tallies showed, as the opposition that campaigned against his strongman approach failed to make the cut.

Monday's ballot for more than 18,000 posts, among them hundreds of mayors, governors, and congressmen, was billed as a referendum on the firebrand president, with special focus on his bid to consolidate power in an upper house that has not always worked in his favor.

A Senate majority would cut the chance of censures and house investigations against his government, making it easier to co-opt independents and remove the few remaining hurdles to an ambitious agenda for massive infrastructure spending, re-drafting the constitution and the return of the death penalty.

"This president's popularity and transferability of his popularity is unprecedented to say the least, despite all the controversies," said political analyst Edmund Tayao.

"You expect normally two or three candidates from the opposition to win, but this is a wipe-out."

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Candidates leading the Senate contest include Duterte's closest aide, the daughter of late dictator Ferdinand Marcos, the wife of the country's richest man, a movie star, a jailed politician recently cleared of plunder charges, and a police general who spearheaded Duterte's brutal war on drugs.

They would join 12 Senate incumbents, only four of whom are from the opposition, including Leila de Lima, the biggest critic of Duterte's deadly anti-drugs crackdown, held since 2017 on narcotics charges.

OPPOSITION DECIMATED

The mid-term results leave the opposition in tatters and will change the dynamic of a Senate that has traditionally been a check on state power, and a bulwark against the kind of political dominance Duterte is demonstrating.

He is also expected to retain control in the lower house.

Presidential spokesman Salvador Panelo said the Senate's independence would not be in question, but the vote showed the public overwhelmingly backed Duterte and his vision.

"Undoubtedly, the Duterte magic spelled the difference," he said. "People yearn for stability and continuity of the genuine reforms that this administration started. They yearn for a constructive and not obstructionist Senate."

The mid-terms come as Duterte, 74, appears untouchable, with last year's spiraling inflation under control and a recent poll showing his public approval rating at a staggering 81 percent.

Experts say the winning formula was selling Duterte as a brand, including use of his daughter Sara as a surrogate to promote his candidates, in a possible succession play for the 2022 presidential election.

The result also shows the effectiveness of a diehard social media support base, despite intermittent outrage over his pro-China stance, jokes about rape, tirades about the church, and his anti-drugs crackdown.

Duterte's critics needed to accept that the electorate had rejected such negative propaganda, Panelo added.

The opposition, however, said it would not give in.

"Our fight for justice, for sovereignty and a more progressive future for our people continues," said incumbent Senator Francis Pangilinan.

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