John Kerry’s emergence as the likely Democratic nominee for president has exposed a sore spot in America’s historical memory – the Vietnam War. That conflict, the nation’s longest, caused far more damage than the 58,235 American troop deaths, thousands more wounded in action, still far more Vietnamese and Cambodian dead and wounded, and a cost of more than $300 billion. It largely destroyed the Johnson and Nixon presidencies, tore apart American society in a cultural revolution, and remains an undigested lump in the national stomach.

Sen. Kerry’s personal record as a decorated Vietnam War hero and later as a leading Vietnam War resister brings the issue to the fore. Democratic charges that President Bush did not fulfill his service in the Air National Guard in that war has put the president on the defensive, but some of Mr. Kerry’s opponents are eager to refight that old war and Mr. Kerry’s part in it.

A recent Wall Street Journal editorial warned ominously that “it is possible to imagine that there are government records from that era that will inevitably make their way into the public debate now that Mr. Kerry has chosen to contrast his Vietnam valor with Mr. Bush’s home-front service.” It went on: “Mr. Kerry will hardly be in a position to cry foul if Republicans seek a full accounting of his public record – in Vietnam and after.”

Fortunately, a respected historian has come out with a book that details John Kerry’s war record and his later leadership of Vietnam Veterans against the War, including the Washington demonstration that culminated in a scene of war veterans, many of them on crutches, throwing away their medals in front of the U.S. Capitol. The book, “Tour of Duty: John Kerry and the Vietnam War,” is by Douglas Brinkley, a professor of history at the University of New Orleans. He relies not only on Mr. Kerry’s own voluminous personal journal but also on more than 100 interviews with U.S. Navy veterans who served with him in Vietnam and fellow demonstrators in the war resistance campaign.

Repeatedly, according to the book, Mr. Kerry was a moderating influence in the fractious veterans’ group, holding back those who tried to provoke a violent clash with authorities and sticking to the main line of nonviolent protest. He comes through as an articulate, courageous, inspiring leader.

Holdouts for the view that the Vietnam War was justified and could have and should have been won are contending that Mr. Kerry was wrong on Vietnam and is wrong on Iraq. (They also complain that he threw away only his ribbons, not his medals. His answer, for those who want to pursue that sideline, is that he was in Washington and the medals were back home in Boston.)

Linking the two wars may seem like an effective anti-Kerry tactic, but it holds risks for the approaching Bush re-election campaign. Mr. Kerry’s record of valor is unquestioned and stands up well against Mr. Bush’s war service. If American casualties continue, and if suicide bombers keep disrupting the effort to bring freedom and democracy to Iraq, the Bush campaign will contend with perceived similarities with an earlier war that was based on faulty intelligence and ended in a forced American withdrawal.