At least three to five constitutional experts, likely retired Supreme Court (SC) justices, are poised to be tapped by the Senate impeachment court to help resolve the divisive debate over the number of votes needed to convict Vice President Sara Duterte, ahead of a possible impasse among senator-judges as to whether to stick with the 16-vote threshold.

Senate President Win Gatchalian told reporters on Wednesday that the court prefers to select “former Supreme Court justices” and “constitutionalists” as amici curiae (friends of the court) to assist them in settling the dispute on whether the required two-thirds for conviction should be calculated based on the total 24 senators or only those currently in office.

Impeachment court spokesperson Reginald Tongol ruled out the possibility of inviting incumbent SC justices to avoid a possible conflict of interest if the contentious issue eventually reaches the high court. 

Gatchalian declined to speculate whether the impending decision on the threshold could raise constitutional concerns and prompt the SC to meddle amid fears that giving a new interpretation of the two-thirds conviction goes against the Constitution. 

“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,” the Senate leader said. 

The impeachment court scheduled a whole-day meeting with amici curiae for 16 September. The issue will be put to a vote by the senator-judges after the defense and prosecution panels have presented their respective positions in oral arguments, which will be held on the same day.

Former chief presidential legal counsel Salvador Panelo, a known ally of the Dutertes, contended that the impeachment court has “no power to change the language of the Constitution.” 

He argued that the base number of senator-judges is fixed at 24, unless one resigns, is expelled, or dies. 

On the contrary, former Ateneo School of Government dean Tony La Viña asserted that the Senate impeachment court can independently decide the matter, as the Constitution vests in it the sole authority to try impeachment cases.

“If there is an appeal on the Senate ruling on threshold, the Supreme Court should dismiss such appeal—regardless [of whether] the traditional or a new interpretation is adopted—on the ground that this is a classic political question which was specifically and exclusively given to the Senate to answer,” his Facebook post reads.

Senator Erwin Tulfo asked the impeachment court on Tuesday to review the 6 July impeachment court’s ruling that upheld the 16-vote conviction threshold, citing the prolonged absence of several senator-judges from the trial. 

The Constitution requires two-thirds—equivalent to 16 votes—of the 24-member Senate to convict an impeached official. 

Since Senators Jinggoy Estrada and Rodante Marcoleta are detained on plunder charges, while Senator Bato dela Rosa remains in hiding to evade an International Criminal Court warrant, they have been unable to attend the trial since it started on 6 July. Senator Loren Legarda, meanwhile, has been on medical leave since 3 August amid a preliminary investigation by the Ombudsman into plunder and graft complaints. 

In a separate interview on Wednesday, Senator Ejercito said he personally prefers the SC to settle the issue on threshold, although he noted that the Senate is also empowered to do so.

Senator Pia Cayetano had warned that reopening the discussion on the 6 July ruling risks rendering it “unconstitutional,” since the Senate impeachment court had already made a decision and must abide by it, unless the verdict is appealed to the SC.

Cayetano urged the Senate impeachment court to decide whether to allow Estrada and Marcoleta to participate and cast their votes despite their detention.

Ejercito, however, echoed Senator Raffy Tulfo’s concern about their possible late entry to the proceedings, considering that the trial has already entered its second month.

Gatchalian said the request to allow Estrada and Marcoleta to participate in the trial rests solely with their respective parties—not the Senate—consistent with past practice.

This stood in stark contrast, however, to presiding officer Chiz Escudero’s statement on Tuesday that it would be the Senate, as a legislative body, to decide whether to convince the Sandiganbayan, as requested. 

“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,” Gathcalian stressed.

The impeachment court intends to conclude the trial and hand down a verdict against the VP by December, in time for the passage of the 2027 budget.