India, July 16 -- Vice President of the United States JD Vance sought last week to use a Marine Corps helicopter to ferry his elementary school-aged son across Washington for a golf lesson, a plan that was quietly seething among Secret Service agents even before severe thunderstorms forced it to be abandoned.

The incident has now emerged as the most vivid illustration of what multiple sources described as a "building morale crisis" inside the US Secret Service detail tasked with protecting America's second family.

The planned trip aboard Marine Two, the call-sign for the US Marine Corps helicopter that carries the vice president, would have carried Vance and his son from the Naval Observatory to the world-class golf centre at Joint Base...