MANILA, the Philippines — Philippine President Ferdinand Marcos Jr. vowed Monday to fight back against what he called reckless and troubling threats against him, speaking out after his estranged vice president said he would be assassinated if she herself were killed.

In a strongly worded video message addressing the nation, Marcos did not name Vice President Sara Duterte, his presidential running mate, but said “such criminal plans should not be overlooked.”

In a dramatic twist in the…