Manila (AFP) - The Philippine Senate opened Vice President Sara Duterte’s impeachment trial on Monday, with her political career – and a planned 2028 presidential run – in the balance.

Thousands of police were deployed around the Senate to provide additional security for the trial as as protesters calling for Duterte’s conviction began gathering outside.

About an hour before the hearing began, the vice president’s office said she would not appear in person.

“We, her lawyers, are here … to prove the allegations against her have no basis,” Michael Poa of Duterte’s defence team told reporters.

In a statement, Duterte said the decision to “appear through counsel rather than testify personally does not diminish accountability or imply a lack of transparency”.

The House of Representatives impeached the 48-year-old daughter of former president Rodrigo Duterte on May 11 on allegations of graft, corruption, bribery and an alleged assassination plot against one-time ally President Ferdinand Marcos.

But only a guilty verdict by two-thirds of the bitterly divided 24-seat Senate can strip her of the vice presidency and permanently bar her from elected office.

Duterte still enjoys public support, with a public survey released in late May showing her as the front-runner in the 2028 race, with 51 percent of respondents saying they planned to vote for her.

The articles of impeachment focus on misappropriation of public funds, unexplained assets, bribery of public officials and the alleged death threat against Marcos and other family members.

The threat against Marcos stemmed from a late-night news briefing in which Duterte claimed to have hired an assassin to kill the president should he have her cut down first.

It will be the focus of the initial stages of the trial, which could take months if prosecutors are given their requested 62 days to present evidence.

- A Senate in turmoil -

Hours before the trial began, a senator who would have served as one of its judges became the second Duterte Senate ally arrested on corruption charges in just over a month.

Senator Rodante Marcoleta’s decision to turn himself in was the latest in a series of institutional shocks at the Senate.

In May, Marcoleta and 12 others lawmakers aligned with Duterte took control of the Senate barely an hour before the House impeachment vote, a move that was later reversed amid a boycott by the vice president’s allies.

One of them, Senator Ronald Dela Rosa – enforcer of her father’s bloody drug crackdown – briefly took refuge in the Senate building as officers attempted to execute an International Criminal Court (ICC) warrant against him.

He disappeared after a tense standoff that saw Senate security guards fire shots.

Another pro-Duterte senator, Jose “Jinggoy” Estrada, was arrested on June 1 for allegedly receiving kickbacks worth more than 573 million pesos (nearly $33 million) over a flood control project.

The Philippine constitution requires a guilty vote by “two-thirds of all the members” of the Senate to convict, but impeachment prosecutor Representative Gerville “Jinky” Luistro has argued the threshold should only include senators who are physically present.

Even if the formula were adjusted, however, Cleve Arguelles of pollster WR Numero told AFP he did not believe the numbers are there to convict.

“I think it’s quite clear that there is a very difficult pathway to conviction,” he said.

- Dynasties at stake -

While President Marcos has taken care to publicly distance himself from the impeachment process, it has unfolded against the backdrop of a blistering political brawl between the Marcos and Duterte dynasties.

A long-simmering feud exploded into open warfare last year with Duterte’s first impeachment – later overturned by the Supreme Court – and the subsequent arrest and transfer of her father to face crimes against humanity charges at the ICC.

“All of these factions are fighting for their political futures,” WR Numero’s Arguelles said.

“For the Marcos administration… they have to make sure that the next administration won’t go after them.”

And even if Duterte avoids conviction, she is unlikely to emerge unscathed after months of intense public scrutiny that could cost her “at the very least, the support of the independents or the moderates”, Arguelles said.