At least three to five constitutional experts, likely retired Supreme Court (SC) justices, are poised to be tapped by the Senate impeachment court as amici curiae (friends of the court) to help resolve the divisive debate over the number of votes needed to convict Vice President Sara Duterte.

Senate President Sherwin Gatchalian said Wednesday that the court prefers “former Supreme Court justices” and “constitutionalists” to weigh in on whether the two-thirds requirement should be based on the full 24-member Senate or only on senators currently able to participate in the trial.

Impeachment court spokesperson Reginald Tongol ruled out inviting incumbent SC justices, citing a possible conflict of interest if the issue eventually reaches the high court.

Gatchalian declined to speculate on whether the Senate’s eventual decision could raise constitutional concerns.

“Let’s just wait and see. It is very difficult to preempt on the board. It depends on the explanations provided by the experts or the amicus curiae,” he said.

16-vote threshold

The impeachment court initially upheld a 16-vote threshold on 6 July, based on the constitutional provision requiring “the concurrence of two-thirds of all the Members” of the Senate to convict an impeached official.

Senator-judge Erwin Tulfo has since asked the court to revisit the ruling and clarify which senators may validly vote when the case reaches final judgment, citing the prolonged absence of several senator-judges.

Senators Jinggoy Estrada and Rodante Marcoleta have been detained on plunder charges, while Sen. Ronald “Bato” dela Rosa remains in hiding to evade an International Criminal Court warrant. Both have been unable to attend the trial since it began on 6 July. Sen. Loren Legarda has been on medical leave since 3 August amid an Ombudsman preliminary investigation into plunder and graft complaints.

The impeachment court is set to hear from the amici curiae during a whole-day session on 16 September, with the prosecution and defense expected to present their respective positions in oral arguments before senator-judges vote on the issue.

Experts divided

Legal experts remain divided over the threshold.

Former SC justice Adolfo Azcuna and UP College of Law Associate Dean Paolo Tamase support retaining the 16-vote threshold, arguing that “two-thirds of all the Members” refers to the full 24-member Senate regardless of who is present.

Former Integrated Bar of the Philippines president Domingo Cayosa and other legal experts, meanwhile, contend that the threshold should be based on senators who can actually participate in the proceedings, which could lower the number of votes required.

UP law professor Dante Gatmaytan said the question remains unsettled because the SC has no ruling directly determining how many votes are constitutionally required to convict an impeached official.

“Technically, the issue of how many votes are required to convict a person who has been impeached has not been settled. There is no Supreme Court decision that answers that question. So, it’s open,” Gatmaytan said.

He rejected arguments that existing SC jurisprudence had already settled the matter, saying cases such as Avelino v. Cuenco and Bayan v. Zamora did not address the number of votes needed in an impeachment conviction.

Who has final say?

Gatmaytan said the Senate, sitting as an impeachment court, has the constitutional authority to interpret the provision because it has the “sole power to try and decide all cases of impeachment.” However, he noted that the SC also has the power to interpret the Constitution and exercise judicial review.

Former Ateneo School of Government dean Tony La Viña likewise maintained that the impeachment court can independently resolve the issue under its constitutional authority.

Sen. Francis “Chiz” Escudero, the impeachment court’s presiding officer, earlier said the Senate would determine the matter. Sen. JV Ejercito, meanwhile, said he personally preferred that the SC settle the threshold issue, although he acknowledged that the Senate is also empowered to do so.

Sen. Pia Cayetano warned that reopening the 6 July ruling could create constitutional complications because the impeachment court had already decided the matter. She also urged the court to determine whether detained senators Estrada and Marcoleta should be allowed to participate and vote.

Gatchalian, for his part, said requests for Estrada and Marcoleta to attend the proceedings should be made to the impeachment court.

“Seek permission from the court because they are under the court’s jurisdiction. Thus, it is the court that will decide whether there is justification for them to attend — whether it be a regular session or the impeachment proceedings,” Gatchalian said.

Beyond Duterte

Gatmaytan said the dispute goes beyond Duterte’s impeachment and should be definitively resolved to guide future cases.

He said the Constitution’s framers may not have anticipated a situation in which senator-judges become unavailable because of criminal proceedings, detention or other circumstances.

He also questioned whether senators who had not attended the proceedings should be allowed to vote on Duterte’s guilt or innocence.

“I think it will be a mockery of the entire system if we allowed people who were never present and were able to appreciate the evidence or the testimonies to come in suddenly and be allowed to vote,” he said.

Tulfo has warned that failure to resolve the issue could result in an “acquittal by default” if the number of senators available to vote falls below the required threshold.