The nation increasingly is being rent by the war in Iraq. The polls demonstrate it, the passions in everyday conversation show it, the political rhetoric in Washington reflects it.

And though the polls, the passions and the politics are genuine, the whole debate over Iraq has the musty feel of an old script. We know what the president will say (stay the course); we know what the opponents will say (an immoral war fueled by lies). We even know what Joan Baez will sing (where have all the flowers gone?). This is a remake of a movie that was filmed when John F. Kerry and Donald H. Rumsfeld were young.

I’ve argued here previously that the Vietnam War was substantially different from the Iraq war. On the surface, they are similar in that neither is technically a war, and both are controversial at home and abroad. But the Iraq conflict is principally urban (Vietnam was mostly rural), it is not a proxy war in a superpower confrontation (Vietnam was an important marker in the Cold War), and its American combatants are in one form or another volunteers (Vietnam’s troops included vocal if not large groups of reluctant warriors resentful of their plight). These conflicts are as different as the desert and the jungle.

That doesn’t seem to matter. The power of Vietnam in American culture – the hurt that lingers, the perceptions that endure – is so irresistible that we have, against all evidence and all reason, reshaped Iraq to look like Vietnam. It is an impulse that cannot be suppressed, though it dishonors the integrity of the arguments on both sides of both conflicts.

But since we apparently insist on forcing the square pegs of Iraq into the round holes of Vietnam, both sides should at least try to avoid the mistakes of Vietnam – and we can all agree, at this distance, that Vietnam was riddled with mistakes, and that the government that prosecuted the war and the protesters who sought to end it made tactical, strategic and ethical errors in their efforts.

The credibility gap. The chasm between what the government claimed in Washington and Saigon and what soldiers saw at Khe Sanh and Hamburger Hill was so great that the moral authority of the Johnson and, later, Nixon administrations was fatally undermined. The Bush administration made a bad start of it in Iraq with its empty rationale that the war was designed to root out Saddam Hussein’s weapons of mass destruction, weapons that didn’t exist and for which evidence was scant and perhaps specious. American support for the war, increasingly fragile, will collapse if the administration isn’t utterly forthright about the progress and the challenges in Iraq in the months ahead.

Blaming the military. One of the saddest aspects of Vietnam was the hostile reception some veterans received when they returned from the battle theater. This scarred them and disgraced the nation. Thus far, those who revile this current conflict have been careful to express their opposition to the policy but their support for the men and women who are carrying it out in difficult circumstances half a world away. Our combatants deserve no less.

Overdefining the conflict. One of the defining errors of the Vietnam War was how it was overdefined. From the Eisenhower administration through the Nixon administration, American strategists argued that Vietnam was but a domino, and that if it tumbled to communism, other dominos would in turn fall. Today substantial numbers of strategic thinkers believe the Bush administration is overreaching with its argument that American soldiers are fighting terrorists in Iraq so they don’t have to fight them in Indianapolis.

Transforming social action into social life. The early days of the anti-Vietnam protests were dominated by committed, thoughtful activists either troubled about America’s prospects for success in Southeast Asia or repelled by America’s actions in Southeast Asia. As the movement swelled, the protest movement became something of a social happening, weakening its moral authority. Cindy Sheehan began a lonely protest out of sadness and sentiment in their purest forms. If her place at the ramparts in Crawford becomes the place to be seen, her place in the American pantheon of protest will be less exalted.

Converting the war into a litmus test of human virtue. On Iraq as on Vietnam, passions are high; for many people their support or opposition to the war represents the signal moral cause of their lives. A generation ago, those passions – significant, legitimate, sincere – prompted blindness rather than insight, causing Americans to regard those who opposed their viewpoints on Vietnam as moral reprobates. These are difficult issues in difficult times; sometimes it is just as difficult to remember that those on the other side may have reached their conclusions through honest deliberation of ethical issues and sober calculation of American interests.

Those were the days. With both sides reading from scripts published in the 1960s and early 1970s, there is an inevitable tinge of nostalgia in the new moral struggle over Iraq, curious to many of us who remember that period as one of bitterness, deception and strife. Even so, there is a misty-water-colored-memories quality in the way war supporters and war opponents are playing their 20th-century roles in the 21st century.

The supporters of military action are determined to do it right this time, to apply adequate force to win and not merely to pour in sufficient troops to assure that the United States does not lose. The opponents of military action are hungry to relive the days of conscience and conflict on campus.

Both impulses suffer from the fatal error of military conflict: They’re fighting the last war.