Philippine senators voted on Tuesday to return an impeachment case against Vice-President Sara Duterte to the lower house to clarify its constitutionality, in a surprise move just hours after convening a trial that could end her political career.

After heated debates, the senators agreed 18-5 not to terminate the trial, but first send it back to the House of Representatives to certify that its handling of the process had been lawful.

However, a member of the lower house said on Wednesday they are deferring response or further action until after getting clarification from the Senate.

"No one can stop this anymore, because jurisdiction has been acquired already by the impeachment court," said Congresswoman Gerville Luistro, pointing to the Senate's issuing of a summons for Duterte.

The House of Representatives impeached Duterte in early February on charges of graft, corruption and an alleged assassination plot against former running mate President Ferdinand Marcos Jr and his family. Duterte has denied all allegations.

Luistro said the lower house's prosecution panel "maintains our position".

"We followed fully and strictly to the requirements of the Constitution," she said.

"What we want to do is to seek guidance and enlightenment first, so we can properly comply with the order of the impeachment court."

Senate President Francis Escudero said the impeachment complaint was not being dismissed. However, some senators, including opposition Senator Risa Hontiveros, said it is the Senate's duty to try to decide the case immediately.

Presidential run

Duterte is widely expected to run for president in 2028 if she survives impeachment, a possibility with deep implications for the political futures of the senators tasked with deciding her fate.

"Governance often takes a backseat to maneuvering for 2028," said Enrico Gloria, an assistant professor of international relations at the University of the Philippines, alluding to how politicians are acting with the 2028 national elections in mind.

Dennis Coronacion, chairperson of the Department of Political Science at the University of Santo Tomas in Manila, was skeptical that the response of the Senate impeachment court would be different in the incoming 20th Congress.

"I think the composition and voting pattern of our senators will not change," he said, noting the Senate's decision to remand the case to the lower house has divided public opinion. Duterte's supporters, he said, are "probably rejoicing".

Duterte is the fifth top official in Philippine history to be impeached, and one of the most high-profile cases.

Agencies and Xinhua contributed to this story.

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