He sought to remain in the Senate for as long as he could, even faced with a diagnosis of aggressive brain cancer.

WASHINGTON — John Sidney McCain III had but one employer throughout his iconic and tempestuous career: The United States of America.

It was a family tradition. McCain was a direct descendant, he claimed, of a captain in George Washington’s army during the Revolutionary War.

And like his father and grandfather before him, each four-star admirals named John McCain, he lived in the service of his country: first as a US Navy fighter pilot, then as a lawmaker until his death Saturday at age 81, following a brain cancer diagnosis in the summer of 2017.

He too might have become an admiral, if a Soviet-made surface-to-air missile had not cut short his own high-flying military trajectory on 26 October 1967.

On the day of his 23rd mission over Vietnam, his A-4 Skyhawk was hit as he flew across Hanoi’s skies.

McCain ejected and parachuted into a small lake in the center of town, where he was nearly lynched by a furious mob. His two arms and right knee were badly broken.

With his father the commander of all US forces in the Pacific, McCain would remain a prisoner of war for more than five years.

He was released in 1973 after the Paris Peace Accords, but the physical consequences of his deliberately ill-treated fractures — and torture in prison — would cost him his career as a pilot.

That something, it became clear, would be politics. After a few years as the Navy’s Senate liaison, McCain moved to Arizona, the home state of his second wife, and won a seat in the US House of Representatives in 1982.

His ambitions grew and he rose quickly to the Senate, the most powerful political body in America. It became his second home for 30 years.

McCain long cultivated the image of a Republican maverick, defying his party on issues ranging from campaign finance reform to immigration.

It was this unorthodox, unbridled McCain, disdainful of authority and occasionally arrogant, who threw his hat in the ring in the two presidential races.

McCain was twice defeated by George W. Bush and Barack Obama.

Trump’s election seemed to trample on the struggles and ideals of the veteran Republican, who quickly grew dismayed by the billionaire businessman’s nationalism and protectionism, his flirtation with Putin and his seeming contempt for the dignity of the office of president.

He even took issue with Trump’s multiple draft deferments during the Vietnam war, granted after he was diagnosed with bone spurs in his foot.

But none of it made McCain want to recede into happy retirement. McCain sought to remain in the Senate for as long as he could, even faced with a diagnosis of aggressive brain cancer.

Since December 2017, he was kept away from the Senate floor as he underwent treatment in Arizona — and received at his ranch a steady stream of friends and colleagues come to bid him farewell, away from the media gaze.

On the eve of his death, his family announced that he was ending his treatment.

McCain let it be known in his memoir published in May, The Restless Wave, that he wished to be laid to rest in Maryland, near his old Navy pal, Chuck Larson.

He is survived by his wife Cindy and seven children, three of them from a previous marriage.