Senator Kerry knows how to make an entrance. When he arrived here in Boston on Wednesday to accept the Democratic presidential nomination, the Massachusetts senator chartered a ferry across Boston Harbor. It was quite a sight.

There’s nothing special about taking a ferry across Boston Harbor, of course. What made the ferry trip special was Mr. Kerry’s traveling companions: a group of Vietnam veterans who had served with the senator 30 years ago along the rivers and rice paddies of the Mekong Delta.

The trip evoked Mr. Kerry’s former days as a Swift Boat captain. It projected an image of strength and resolve. And it was more than an exercise in nostalgia. It showed that Mr. Kerry, like President Bush, would be a war president.

Indeed, it sometimes seemed this week that all the Democrats wanted to do was talk about the war. You heard the word “strength” a lot at the Democratic National Convention. You heard retired generals proclaim their support for Mr. Kerry and veterans champion the senator as one who “knows what war is like.” You heard Teresa Heinz Kerry say her husband won his medals “the old fashioned way.”

The war the Democrats wanted to talk about wasn’t the war on terrorism, however, or the war against the Taliban, or the war in Iraq. It was the Vietnam War. And it is nothing new.

When I saw Mr. Kerry and Senator Edwards campaign in south Florida earlier this month, neither candidate mentioned Iraq at all. Not once. The same went with the war in Afghanistan. But Vietnam? It came up again and again.

This isn’t a coincidence. Talk to Democratic strategists, and they tell you that Mr. Kerry’s war heroism long ago insulates him from criticism that he is soft on national security today.

Mr. Kerry’s Vietnam experience “is part of his life, it’s part of his history, it’s part of who he is,” senior Kerry adviser Bob Shrum told reporters here yesterday.

Mr. Edwards said the same thing in his Wednesday address: “When a man volunteers to serve his country, a man volunteers and puts his life on the line for others, that’s a man who represents real American values.”

In politics, you’re either on offense or defense. There is an offensive component to all this talk of Vietnam. Democrats want to draw attention to the fact that Mr. Bush has never been in combat – that he occasionally did not show up for National Guard duty 30 years ago, in fact.

“The Bush people can talk about that issue if they want,” Mr. Shrum said yesterday, an impish smile on his face.

But there’s a defensive component too. What the Kerry campaign doesn’t want to talk about is the senator’s voting record on national security issues. So they talk about Vietnam instead, using that war to block the volleys from the Republican opposition research team.

Here is a small sample of what the Kerry campaign is up against: In the 1980s, when he first came to the senate, Mr. Kerry voted against President Reagan’s support for anti-Communist forces in Central America.

In the 1990s, Mr. Kerry voted against the first Gulf War, and then voted to cut funding for intelligence and weapons programs.

In 2002, he did vote for the second Gulf War, but then he went and voted against last year’s $87 billion appropriation for reconstruction in Iraq and Afghanistan.

This may be why the war that Republicans want to talk about is the war on terrorism. Witness Vice President Cheney’s remarks to marines at Camp Pendleton this week, for example:

“This nation has made a decision. We will

engage the enemy – facing him with our military in Iraq and Afghanistan today, so we do not have to face him with armies of firefighters, police, and medical personnel on the streets of our own cities.” That’s the message uttered every day by the president and his surrogates.

When Mr. Bush says he is a “war president,” he’s not discussing his autobiography. He’s reminding the public that he toppled the Taliban in Afghanistan and the Baathists in Iraq.

It’s when conversation turns to Mr. Kerry’s position on the war in Iraq today – as in the classic moment when Mr. Kerry said he “actually voted for the $87 billion before I voted against it” – that Mr. Bush looks his decisive best.

Sure, the Democrats took great pains this week in Boston to show they are well equipped to handle the challenges we face in an age of terrorism. They were largely successful in doing so.

But if you asked Democratic delegates the first thing that comes to their mind when they hear the name John Kerry, you heard the same answer again and again: “Vietnam.”

It’s troubling. The Democrats talk about Vietnam while the Republicans talk about Iraq and the war on terrorism. It’s as if you had three wars going on all at once: One in Iraq, one in Afghanistan, and then another in Indochina.

The question is this: Which war will Americans find more important? The troubled war long past, or the troubling war today?

We’re told the Vietnam War ended 30 years ago with the fall of Saigon. But it didn’t, really. Or at least the Kerry campaign doesn’t think so.

The Kerry campaign believes the memory of that war lives on and that they can ride distant memories of glory and sacrifice to victory.