The people like Kennedy who are trying to draw an analogy to Vietnam aren’t trying to make obscure points about tactical similarities or differences - they are trying to claim that Iraq is a ‘quagmire’ like Vietnam - one which will go on forever, consume tens of thousands of U.S. soldiers, and be unwinnable.
So when making the comparison, let’s look at the major reasons why the U.S. ‘failed’ in Vietnam, and why that won’t happen in Iraq.
First, the Vietnam was was fought under strict rules of engagement that severely hampered the U.S.'s ability to fight.
Second, South Vietnam was under assault from a huge army in North Vietnam, which the U.S. was not really able to go after in a major way for political reasons.
Third, North Vietnam and the Viet Cong were heavily supported by China and the Soviet Union. This, coupled with the U.S.'s strategic inability to occupy North Vietnam due to risks of drawing superpowers into the conflict, meant that the U.S. was fighting a war of attrition against an enemy with an almost limitless resupply capability.
The goals of the Vietnam war were different. The U.S. was not trying to destroy an army and pacify a country - it was essentially engaged in a battle of wills against a determined enemy to see who would quit first.
Vietnam was fought in mountainous and jungle terrain which is the natural fighting ground of guerillas, and which negated much of U.S. air power.
If the Soviet Union and China had not been in the picture, the U.S. could simply have bombed the industrial infrastructure of North Vietnam, invaded, destroyed the North Vietnamese army, and South Vietnam would have survived.
If you read about the Vietnam war, what strikes you is that it was fought almost as if the U.S. didn’t want to win it. For example, the Ho Chi Minh trail, which was a primary enemy resupply conduit, was largely off limits to strategic bombing. Operation “Rolling Thunder” did bomb one of the passes leading into the trail, but the purpose was not to destroy the supply lines, but to put pressure on North Vietnam to come to the negotiating table. This theme persisted throughout the Vietnam war - military power used as a negotiating tactic rather than to achieve a military outcome. People like Curtis Lemay were quite upset about this, because they believed that once you go to war you fight to win, and he wanted to bomb all the entry points to the trail, turn the trail itself into a free-fire zone, and bomb the North Vietnamese infrastructure.
This politicization of military power was the prime motivator behind the 'Powell Doctrine", which the U.S. operates under now, which essentially says that you do not go to war unless A) you are willing to do whatever it takes to win it, and B) you have an exit strategy. That doctrine came right out of Powell’s experience in Vietnam.
And consider the quality of the average soldier at the time. Vietnam was fought by a conscript army that didn’t really want to be there. In Iraq, the armed forces are comprised of an all volunteer professional force with high morale and unsurpassed capability.
Look at the difference in technology - There were no ‘smart bombs’ in Vietnam. The only way to hit strategic targets from high altitude was to carpet bomb it. Urban warfare was immensely destructive.
Now look at today. Iraq is a desert - there is nowhere for Guerillas to hide other than within the population in the cities. There is no superpower supplying them. The lessons of Vietnam HAVE been learned, and as a result ground commanders are given wide lattitude in how and where to engage the enemy. Precision bombing, satellite imagery, unmanned drones, and the like give the U.S. military huge advantages, even in urban conflict. Today, advances in sensor technology and smart weapons allows air power to be used in urban warfare by striking precisely on targets illuminated by lasers from ground forces, minimalizing collateral damage.
Look at the war in Fallujah so far. Less than ten U.S. soldiers killed so far (I think the number is five or six), vs at least 450 dead insurgents. They don’t have a chance. And they can’t sneak out of the city, and they can’t sneak in supplies and ammunition. The U.S. military totally controls the area around the city, and can maintain that control indefinitely.
So almost none of the things that caused the Vietnam war to be a failure exist in Iraq. The biggest being that Vietnam cost 58,000 American lives, and the toll after a year in Iraq is just over 600. Huge difference. In WWII the U.S. lost 12,000 soldiers just taking the island of Okinawa. The total loss of soldiers so far in Iraq was lost about every six days in WWII. So on a historical scale, the Iraq war is a tiny conflict. It’s clearly within the U.S.'s capability to do whatever it takes to win.
Now, that’s not to say there aren’t other difficulties in winning in Iraq - there are plenty. The point is that the Vietnam analogy is pointless and wrong, and is only being employed as a scare tactic.
Which brings us to the only real valid comparison between the two - the U.S. lost in Vietnam in part because the media constantly mischaracterized the nature of the war, and because opponents at home sapped the will of the country. Take the Tet Offensive - it was a massive military defeat for the Viet Cong - they essentially ceased to exist as a fighting force after that. The American military mopped the floor with them. But the media portrayed it has a victory for the Viet Cong, and as a defeat for the Americans.
The same thing could easily happen in Iraq. Take the current uprising - it’s not a widespread Shiite uprising - it’s a band of radicals with an illegitimate ‘cleric’ as a leader, who has cast his lot in with various terrorist factions and ex-Saddamites. The U.S. military is going to crush them like bugs. They will heavily lose every battle they fight, and they will continue to be destroyed until they stop fighting or there are none left. But the media may wind up portraying it as a general uprising, and show every civilian casualty, the execution of every hostage (I believe there will be some), and in the end it could wind up as a ‘loss’ for the U.S.
The main lessons of Vietnam are being used by the enemy. They are going to fight this war in the media. In that sense, a better analogy is the Palestinian intifada. They know they can’t win against U.S. forces, so they are going to make this war as grotesque as possible, hoping that the American media’s sensational reporting causes the population to lose its stomach for the conflict. Hence the hostages, the bodies hanging from bridges, etc.
Comments like Kennedy’s are exactly the kinds of responses they are looking for, and comments like that from high-ranking lawmakers are simply going to embolden them and encourage them to do even more despicable acts. This is why Colin Powell broke his policy of not getting into political commentary and basically told Kennedy to shut his mouth. His comment was irresponsible.