Philippine presidents rise and fall on one issue — corruption.

The classic example was Ferdinand Marcos who ruled the country with an iron fist for 20 years until the people rose in a peaceful uprising in 1986.

Out of fear of a dictator, many people kept silent for years, despite hearing stories of the astonishing extravagance of Marcos family members and cronies helping themselves to the country’s coffers while the government was buried neck-deep with debt.

When Marcos hastily left, whisked away by American military helicopters to Clark Air Base first, then finally to Hawaii, the extent of his corruption unraveled.

An estimated $10 billion was stashed away in secret bank accounts in Switzerland. There were precious jewelry collections, artwork that could rival the National Museum’s, and properties and shares of stock here and abroad.

Filipinos’ hatred for a corrupt regime swept to power the wealthy widow of an opposition politician who was assassinated three years earlier. She was immaculately graft-free and remained clean up to the end of her six-year term in 1992.

Many of her followers would have her declared a saint but not the people around her, as corruption reared its ugly head once more.

It was an election issue in May 1992, causing the downfall of Speaker Ramon Mitra, the Palawan congressman who controlled the House of Representatives, which was derided by the public as a house of thieves.

Two presidential hopefuls — a West Point-trained army general known to be as straight as an arrow, Fidel Ramos, and anti-corruption crusader Miriam Defensor- Santiago — battled for the coveted seat in Malacañang.

Ramos, of course, won narrowly over Santiago, who said she was cheated of electoral victory.

Ramos was succeeded by an immensely popular movie action hero Joseph Estrada, but less than three years later, he was forced to resign over corruption issues.

Philippine media went to town exposing Estrada’s palatial mansions, including one that imported sugary white sands from Boracay complete with a machine that created ripples of waves on a swimming pool.

Estrada denied stealing from government funds but was accused of taking bribes and kickbacks from gambling lords and tobacco farmers as well as insider trading in the stock market.

He was replaced by Gloria Macapagal Arroyo, his vice president, in accordance with the 1987 Constitution. Her reputation was also murky because of the people around her.

She was in power for nine years but for more than half of those years, she was struggling to fight off the impeachment process in the lower house and a restive military that attempted to remove her several times.

Arroyo was accused of stealing the elections in 2004 after the leak of a phone conversation between a woman who sounded like her and an election official. A multi-billion peso broadband deal with China’s ZTE Corp. also blew up on her face, linking several people, including the head of the Commission on Elections.

She did finish her term but had the worst performance rating as president, which plunged to minus 50 at one point at the height of the bribery scandal.

Fed up with a corrupt government, Filipinos elected Benigno Simeon Aquino III, son of the country’s two democracy icons, a three-term congressman and a three-year senator who had no corruption issues.

He kept his clean image until the end of his term but his allies pulled him down as corruption scandals erupted in many government agencies, including in Congress because of pork barrel, which was renamed “Disbursement Acceleration Program.”

In 2016, Filipinos chose Rodrigo Duterte who was perceived to be an honest and corruption-free politician from the south. His image propelled him to record-smashing satisfaction and trust ratings of above 90 percent, a first in Philippine history.

Duterte may be perceived to be clean but not the people around him, as issues of corruption continued to plague the government.

Presidential candidates also rise and fall on the same issue of corruption.

The Philippines will return to polling precincts next year to elect new leaders and corruption will be the main driver that will decide the fate of presidential aspirants.

Duterte’s record for the last six years will be under intense scrutiny but there’s obviously one measure he should pass — did he take advantage of his position to enrich himself and his family while in office?

There’s little dirt and muck his opponents can throw at him except that Duterte’s government failed in the pandemic response, resulting in millions of Filipinos losing their jobs and livelihoods.

Duterte should be grateful he remained immensely popular as a leader. In another world, he would have been impeached for betraying public trust for reneging on his oath to defend and protect the country’s sovereignty and territorial integrity, when he threw away the country’s landmark legal victory at The Hague against China over the South China Sea.

Duterte’s record as anti-corruption crusader is patchy. He has removed ordinary bureaucrats but never went after people he had appointed to positions of power. He sacked some of them, only to be given other juicy positions. The practice has very little impact on anti-corruption efforts.

Recently, one of his staunch allies, Sen. Emmanuel Pacquiao, turned against him, accusing Duterte’s government of corruption especially in how cash aid was distributed to millions of people during the pandemic.

It is too early to tell the impact of the eight-time world boxing champion on Duterte’s popularity, and whether his “corruption” punches would knock out the leader who has emerged as the top choice for vice president in a pre-election survey in June.

The easiest way to pull down top contenders in the presidential elections is to look for corruption issues.

A former vice president, Jejomar Binay, and a former Senate president, Manuel Villar, who were way, way ahead in pre-election surveys, lost in actual elections due to corruption issues.

That could be one reason why Pacquiao, who aspires to succeed Duterte next year, is trying to demolish the clean image of the president.

Pacquiao’s attempt to sully Duterte’s image signals the start of muckraking in Philippine elections. Pacquiao was only the opening salvo as Duterte’s political opponents are starting to dig deeper into other corruption issues, including those that could personally link him into anomalous transactions.

As president, Duterte could be liable for allowing such onerous deals that are disadvantageous to the government.

If there are politicians who want to stop Duterte from staying in power through his daughter who also topped the pre-election surveys for president last month, they must find damning evidence to show his corruption.

Duterte is vulnerable to corruption issues. He has not publicly declared his statement of assets, liabilities and net worth (SALN). Two chief justices of the Supreme Court fell from grace on the SALN issue. He has admitted to receiving lavish gifts, like a house and a car, as mayor of Davao City.

The race is on, not to take an early lead in pre-election surveys, but to look for a smoking gun, dirt hard enough to shake off and destroy Duterte’s image.