They went through New England prep schools and Yale at the time when the New Frontier collided with the Vietnam War. They came of age at a time young men struggled with big questions of conscience. They entered the work force in an age of rights but at a time when the nation struggled with its limits.

George W. Bush and John F. Kerry might be called the two sides of the baby-boom generation, except for the inconvenient fact that this was a generation for which there was always more than two sides.

Even so, this is the election of a generation.

There were, to be sure, two baby-boom candidates four years ago. But in retrospect, it is clear that the 2000 campaign between Bush and Vice President Al Gore was not so much about the new world and the new era as it was a debate over whether the old ones could, or should, be extended. The bridge to the 21st century, it turned out, was a toll bridge, and not until Sept. 11, 2001, did we pay the toll. Now we see that our politics today are different in form, substance, rhetoric and imagery from the politics of the earlier era, dominated as it was by political figures steeped in World War II and its lessons.

Indeed, in every election from 1944 to 1996, at least one major-party candidate was closely identified with, or had served in, the war. Now these figures have passed from the scene, leaving politicians with different experiences and different worldviews at the helm of both parties.

Much has been written about Kerry and Bush and their attitudes about Vietnam and the protests that were so much a part of domestic life in those years. But what might be even more instructive is to examine how the two men view the nation they seek to govern and the world they hope to shape.

Their fathers — veteran diplomats, both — saw the globe convulsed in conflict, and then, once the peace came, the struggle continued, though in a new form, but it still took the form of a struggle between the democracies and the dictators. But the sons saw how the lessons of the old conflict provided precious few insights for the conduct of the new conflict. Applying the lessons of Munich to the Mekong, for example, proved to be impossible — and tragic.

Bush and Kerry differ on many things, some big, some small. They differ on weapons systems, but presidential candidates almost always do. That’s a small thing. They differ on the precise conditions in which they would project American force in conventional crises among nations, but that is not unusual either. That’s a relatively big thing. They differ on the notion of unilateral, pre-emptive American military action, which is an issue that may be unique to our time. That is a very big thing.

But they agree on one important thing, and it has nothing to do with ideology and everything to do with experience. They agree that the old rules — even the ones they lived by as young men — no longer apply to the crises of American national security. That’s a very important departure. Only rarely in American history have two candidates sought the highest office with bitterly different ideologies but with the shared conviction that the old verities are more old than true. This, the two men agree upon, and it is the fundamental fact of this election.

This was not so when the two major visionaries of the last century, Woodrow Wilson and Franklin Roosevelt, sought office or even when they sought re-election four years later. Their great notions came later, at the end of his presidency in Wilson’s case and at the beginning of his third term in FDR’s. The two ran for office, and then won re-election, with worldviews that were basically consistent with those of the men (William Howard Taft and Herbert Hoover, respectively) who preceded them.

What do Bush and Kerry believe that their fathers and their predecessors did not?

They believe that the entire way of looking at American security, which had been unchanged in character since 1917, is obsolete. From the dawning of America’s engagement in World War I until the evening of Sept. 10, 2001, American presidents worried about other nations, their leaders, their weapons and the stability of those nations and their leaders. President Clinton thought himself a thoroughly modern president, and in some aspects he was, but he, too, was preoccupied with the conventions of statecraft.

The first President Bush was perhaps the most accomplished practitioner of statecraft of his generation. Those tools and those skills still have a place, but now they are on the margins. The current President Bush knows this. So does Sen. Kerry. They have different prescriptions — Bush wants to take on the world himself, and Kerry wants to have some friends at his side — but neither of them uses the phrases of the past: the Concert of Europe, the balance of power, big-power politics, power politics. Those phrases are for the seminar room in the history department, not the situation room in the White House.

And so this election is one of those few that is not about the future but about the present. The future is too scary, and too far away, to worry about this summer and fall, preoccupied as we are with terrorist attacks and the changing nature of security.

Other recent campaigns were full of echoes. What Clinton said about idealism sounded a lot like what John F. Kennedy said. What George H.W. Bush said about taxes sounded a lot like what Ronald Reagan said. That’s the big thing that’s different in this election of a generation. The two candidates are not new on the national scene. The absence of the echoes is.

David Shribman is a columnist for Universal Press Syndicate.