I think Daniel Henninger nails the meaning of John Kerry’s candidacy (and George Bush’s):

"John Kerry was present at the creation of the moral and intellectual voyage of post-1960s Democrats. He helped map its course. He testified in 1971 against the Vietnam War as a young veteran before the Senate Foreign Relations Committee. He appeared as an antiwar spokesman on "60 Minutes" and "The Dick Cavett Show." John Kerry was a celebrity among Primary Democrats as Bill Clinton never was during this important period. As a Southern governor, Mr. Clinton learned about the inevitable left-right compromises of public policy in ways that rarely tainted the austere ideological experience of Mr. Kerry in the liberal northeast and Washington. (This may well disadvantage Mr. Kerry in the election.)

"We have in George Bush a president for whom the formative event of his political life is not Vietnam and the years after but September 11, a catastrophic attack on American soil by an organized global enemy. With his doctrine of pre-emption for threats to U.S. security, his destruction of the Taliban and overthrow of the Hussein regime in Iraq, Mr. Bush has largely broken free of the political period that shaped John Kerry’s career. Mr. Bush argues that he is dealing with a world and enemy that has not previously existed. But with Iraq, 30 years of Primary Democratic belief instinctively reappears as resistance, led again by John Kerry. If George Bush’s sense of right purpose flows directly from September 11, 2001, so too does many Democrats’ from what John Kerry was doing and thinking in 1968 in the Mekong Delta."