MANILA, Philippines — The battle over the voting threshold in Vice President Sara Duterte’s impeachment trial has taken another dramatic turn, with a member of the 1987 Constitution’s framers raising an interpretation that could potentially change how the Senate calculates the votes needed for conviction.
The controversy centers on one phrase in the Constitution: “two-thirds of all the Members of the Senate.”
The Senate impeachment court had earlier ruled that 16 votes are required to convict Duterte, based on the 24-member Senate. But with several senator-judges currently unable to participate in the proceedings, questions have emerged over whether those absent senators should still be included when calculating the two-thirds requirement.
THE 16-VOTE QUESTION
Article XI, Section 3(6) of the 1987 Constitution states that no impeached official may be convicted without the concurrence of two-thirds of all the Members of the Senate. With 24 senators, the traditional computation produces a threshold of 16 votes.
Senate President and impeachment-court presiding officer Francis “Chiz” Escudero previously ruled that 16 affirmative votes are required to convict Duterte.
That interpretation, however, is now being revisited.
Senator-judge Erwin Tulfo questioned what happens if some members of the impeachment court are unable to attend or participate when the final vote is eventually taken. He specifically asked whether senators who are detained, in hiding or otherwise unavailable should be included in the calculation.
WHY THE ISSUE HAS BECOME SO IMPORTANT
The dispute is no longer merely theoretical.
Several senators have been unable to consistently participate in the impeachment proceedings. GMA News reported that four senator-judges were then unable to attend: Ronald “Bato” dela Rosa, Jinggoy Estrada, Rodante Marcoleta and Loren Legarda, although their individual circumstances differ.
That creates a constitutional dilemma.
If all 24 senators remain in the denominator, conviction requires 16 votes.
But if senators who are legally unable to participate are excluded from the computation, the number of votes required could potentially fall.
That distinction could have a major impact on the eventual outcome of Duterte’s impeachment case.
CONSTITUTIONAL FRAMER OFFERS A DIFFERENT VIEW
Former Supreme Court Associate Justice Adolfo Azcuna, who was among the framers of the 1987 Constitution, has previously defended the 16-vote threshold, arguing that the Constitution deliberately says “all” members of the Senate.
Azcuna told GMA News that detention or suspension does not automatically remove a senator from the Senate’s membership, meaning those senators would generally remain part of the calculation.
Philstar also reported Azcuna’s position that the constitutional requirement was designed to make impeachment conviction difficult and prevent the process from being manipulated by simply reducing the number of senators counted.
However, the broader legal debate has produced competing interpretations.
Retired Supreme Court Senior Associate Justice Antonio Carpio, for example, has argued for a different approach—one that considers senators who are legally qualified to participate in the proceedings when determining the applicable two-thirds threshold.
That disagreement is at the heart of the current controversy.
SENATE TO HEAR LEGAL EXPERTS
The issue has become serious enough for the Senate impeachment court to seek outside constitutional expertise.
Escudero announced that the court will hear from amici curiae, or “friends of the court,” before the parties present their arguments. Legal experts and possibly retired Supreme Court justices are expected to weigh in on the meaning of the constitutional phrase.
The impeachment court has scheduled September 23, 2026 for oral arguments involving the prosecution and defense on the voting-threshold question.
The court is therefore expected to confront a question that could become one of the most consequential procedural issues in Duterte’s impeachment trial:
Does “two-thirds of all the Members of the Senate” mean all 24 senators—or only those legally capable of participating and voting?
WHY THE CONSTITUTION MATTERS
The controversy also highlights why impeachment is treated differently from an ordinary legislative vote.
The Constitution gives the Senate the sole power to try and decide impeachment cases and requires senators to take an oath when sitting as an impeachment court. It also expressly establishes the two-thirds requirement for conviction.
The Senate’s own impeachment rules likewise provide that an article of impeachment must be sustained by the votes of two-thirds of all the Members before a conviction can be entered.
The Supreme Court has also recognized the Senate’s constitutional role in impeachment proceedings. In an April 2026 decision involving the Duterte impeachment case, the Court said the Senate’s exercise of its impeachment duties is generally beyond judicial control through mandamus, subject to constitutional limits and possible grave abuse of discretion.
THE BIG QUESTION AHEAD
For now, there has been no final change to the 16-vote requirement.
The Senate impeachment court is still set to consider the competing legal interpretations before determining whether its earlier ruling should stand.
That means the eventual vote on Duterte’s fate could depend not only on how senator-judges view the impeachment charges—but also on who will legally be counted when the final tally is made.
And with the Senate preparing to hear constitutional experts and the prosecution and defense on the issue, one question now hangs over the trial:
Will 16 votes still be enough—or will the Senate ultimately change the rules for determining the number needed to convict?
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