A new front has opened in the political battle over Sen. John Kerry’s military credentials, sparking continued questions and an equally strong defense of the Massachusetts Democrat’s post-Vietnam War actions in the usually stately Senate chamber.

Until this week, Kerry’s ability to serve as commander in chief was debated exclusively on the campaign trail as Republicans sought to distinguish his decorated military service from his voting record and past statements on national defense issues. That ended Tuesday, when Sen. Frank Lautenberg (D-N.J.) delivered an an impassioned but overlooked speech from the Senate floor admonishing his Republican colleagues for questioning Kerry’s defense credentials.

“For years the charge coming from across the aisle is that Democrats are somehow or other less patriotic, less supportive of defense, and it is a shameful and grotesque charge,” Lautenberg said. “In my view these charges typically come from people I would simply call chicken hawks.”

Lautenberg also sought to turn the tables on Kerry’s Republican critics, particularly Sen. Saxby Chambliss (Ga.), who on Saturday criticized Kerry’s voting record on defense issues. While he didn’t specifically name Chambliss, Lautenberg offered an unmistakable reference to the Georgia Republican’s decision to invoke several deferments that shielded him from having to serve during the Vietnam War.

“It is the same easy road we see when someone files for five student deferments and then claims an old football injury should prevent him from fighting for his country,” chided Lautenberg, as he sought to discredit Senators who brandish their national defense credentials by way of votes, but sidestepped military service.

Chambliss dismissed Lautenberg’s comments Wednesday and said such criticism won’t stop him from speaking out in the coming months about Kerry’s voting record.

“You know we have a saying back home that a ‘bit dog barks,’ and we have struck a nerve with the Kerry campaign,” Chambliss said. “They obviously know they have got some weaknesses and this must be one of the places where they think they are weak.”

“What I said was right and every opportunity that I have — or at least when the need is there for me to say it or the issue is there and I am there to say it — certainly I will because I am right,” he added.

While most Republicans have been careful not to question Kerry’s service in Vietnam for fear of inciting anger among veterans, Sen. Larry Craig (R-Idaho) criticized the Massachusetts Democrat’s decision to cast away medals and citations during a 1971 anti-war demonstration.

“I am not in any way going to impugn John Kerry’s military record,” Craig said. “He deserves all of that even though he threw his medals into the Reflecting Pool. That’s OK. He can do that. They were his medals once granted to him.”

When informed that Kerry only threw his ribbons in and the medals in question were in fact those of two other veterans, Craig sharply responded, “I know that. He admitted that later. I believe the medals are somewhere out there at the bottom of a pond.”

Unlike differences over policy issues that rarely take on a personal tone, the disagreement over Kerry’s commitment to national defense has the potential to do irreparable harm to long-standing relationships in the historically collegial Senate. The defense of Kerry is rooted in the 2002 elections, when Chambliss defeated then-Sen. Max Cleland (D-Ga.), a triple-amputee Vietnam War veteran whose patriotism was questioned during the campaign.

Democrats acknowledge they have not been able to move beyond Cleland’s loss.

“We learned a valuable lesson [from] what happened to Max Cleland,” said Sen. Dick Durbin (D-Ill.). “It was a defining moment for the Senate Democratic Caucus when a man who gave both legs and an arm in Vietnam had his patriotism questioned.”

Specifically, Democrats are still simmering over a political ad from the election that sought to link Cleland to Osama bin Laden and Saddam Hussein, because the Georgia Democrat refused to support President Bush’s proposal to create a Department of Homeland Security. Under heavy pressure, Chambliss removed the pictures of bin Laden and Hussein but never took the advertisement down.

In recent months, Cleland has become a prominent surrogate on the campaign trail, touting his support for Kerry’s candidacy. Cleland also cut a 30-second ad that will run in Georgia urging Peach State Democratic voters to support Kerry on Super Tuesday.

Sitting outside the Senate chamber Wednesday, Lautenberg referenced Cleland’s loss several times in explaining why he chose the Senate floor as his stage to defend Kerry. Lautenberg said he told the Kerry campaign of his plan in advance, but described it as an “independent action.”

The New Jersey Senator offered a sheepish laugh when asked why he chose to criticize Chambliss, but quickly shifted the subject back to the GOP’s attacks on Kerry.

“Accusing John Kerry of weakness on defense is actually challenging his patriotism,” Lautenberg said. “What the hell must a man do besides what he did?”

With Super Tuesday just days away, bringing a likely end to the Democratic primary and shifting the race for the White House to the general election, the fight over Kerry’s record is going to intensify, Democrats and Republicans alike acknowledged. A Senate Democratic leadership aide said a formalized effort to defend Kerry would be put in place to shield him from Republican attacks once the primary is over. Durbin provided a more specific game plan.

“We are serving notice on the Republican side — if they are going to question the patriotism or service records of Democratic Senators — our veterans in our Caucus are going to speak out,” Durbin said.

Already, Democrats have raised questions about Bush’s Vietnam War service, which Kerry has mentioned on the campaign trail.

For their part, Republican leaders said they will not be bullied by the Democratic threats and plan to publicize their concerns about Kerry’s record at every turn.

“In a sense we have let the other side dictate this debate for far too long and we are going to stand up,” vowed Senate Republican Conference Chairman Rick Santorum (Pa.). “Now that we have someone we can talk about — they have had someone they can talk about for a while — we are going to talk about this man’s record.”

The heated rhetoric over the Vietnam War has at least one veteran concerned. Sen. John McCain (R-Ariz.), who was shot down and held prisoner by the North Vietnamese, said he has urged both sides to move beyond the argument and focus their disagreements on the future direction of the nation.

“I have spent the last 30 years trying to heal the wounds of the Vietnam War and I am not interested in reopening them,” McCain said.

“I feel very strongly that they should understand by reopening the whole issue of the Vietnam War they can do some harm to some Vietnam veterans.

“I have said publicly to everybody the issues that we should be talking about are the issues of the future, not 30 years ago,” McCain added.