Manila, Sept. 16 -- Wrongfully preventing a senator-judge from taking part in an impeachment trial could expose the entire proceeding - including an eventual verdict - to Supreme Court review and possible nullification, retired Chief Justice Reynato Puno warned Wednesday.

Puno drew a line between matters left solely to the Senate impeachment court and actions that could cross into constitutional violations as he advised senator-judges on the disputed voting threshold in Vice President Sara Duterte's trial.

"One such action, Your Honors, is when the Senate Impeachment Court unjustifiably denies some of its members the right to sit as judges in the impeachment court," Puno said as amicus curiae (friend of the court).

He said the same con...