A quiet retirement for Philippines President Rodrigo Duterte is unlikely when he makes way for successor Ferdinand Marcos Jr., but efforts to put him on trial for thousands of killings in his "war on drugs" appear unlikely to prosper.

Duterte's daughter, Sara Duterte-Carpio, helped get Marcos elected by agreeing to be his vice presidential running mate, allowing the son of the late dictator to tap her father's huge support to seal a comeback for the disgraced Marcos dynasty.

Though there has been no formal quid-pro-quo, political experts say it is unlikely Marcos would risk burning crucial bridges by allowing the International Criminal Court (ICC) to investigate Duterte over the alleged execution-style killings in his war on drugs.