Between them, Senator John Kerry and Chuck Hagel have five Purple Hearts for wounds suffered in Vietnam, shared a harrowing combat experience in the Mekong Delta and responded in different ways to the conflict that tore their generation apart. But in nominating one as secretary of state and the other as defense secretary, President Obama hopes to bring to his administration two veterans with the same sensibility about the futilities of war.

Mr. Kerry, a Massachusetts Democrat who is the president’s choice for the State Department, came home from commanding a Swift boat in Vietnam to throw away his military decorations in a protest at the Capitol, accuse American troops of systematic atrocities and tell the Senate Foreign Relations Committee, “How do you ask a man to be the last man to die for a mistake?”

Mr. Hagel, a former Republican senator from Nebraska who is the nominee for the Pentagon, returned home thinking of the war as justified and did his best to put it behind him. “I wanted a life,” he later said. Mr. Hagel eventually turned against the leadership of the war — “I can’t fathom that this country would allow something like that to happen, 16,000 young men killed in one year,” he told Vietnam magazine, a history publication, in October — but not its warriors. Today he is the chairman of the Pentagon’s advisory group for commemorations of the 50th anniversary of the Vietnam War....