Democratic presidential candidate John Kerry (search) on Saturday night urged President Bush to "stand up and stop" what he called personal attacks on him over his combat record in Vietnam.

At a fundraiser, attended by about 750 people, Kerry said the attacks by a group of Vietnam veterans and former Swift Boat commanders have intensified "because in the last months they have seen me climbing in America's understanding that I know how to fight a smarter and more effective war" against terrorists.

"That's why they're attacking my credibility. That's why they've personally gone after me. The president needs to stand up and stop that. The president needs to have the courage to talk about it."

Swift Boat Veterans for Truth (search), a group funded in part by a top GOP donor in Texas, has been running ads featuring veterans who served in Vietnam at the same time as Kerry and question his wartime record.

The White House and the Bush campaign have denied any direct connection with the Swift Boat group. "The president has made it repeatedly clear that he wants to see an end to all" advertising from outside groups, said Brian Jones, a Bush campaign spokesman.

But on Saturday, a former POW, retired Col. Ken Cordier (search), resigned as a volunteer from the Bush campaign's veterans' steering committee after it was learned that he participated in an anti-Kerry ad sponsored by the Swift Boat group. The ad criticizes Kerry's congressional anti-war testimony in the 1970s alleging U.S. troops engaged in atrocities in Vietnam.

"Col. Cordier did not inform the campaign of his involvement in the advertisement," the Bush campaign said in a statement. "Because of his involvement (with the group) Col. Cordier will no longer participate as a volunteer for Bush-Cheney '04."

Earlier on Saturday, Kerry's campaign released a video comparing the controversy over Kerry's Vietnam service to attacks on John McCain during the 2000 Republican primaries.

The video, sent via e-mail to supporters, says, "George Bush is up to his old tricks" and shows then-Texas Gov. Bush and Arizona Sen. John McCain at a debate in February 2000.

McCain, sitting next to Bush, says that when "fringe veterans groups" attacked him at a Bush campaign function, Bush stood by and didn't say a word. McCain says a group of senators wrote Bush a letter that said: "Apologize. You should be ashamed."

McCain, also a Vietnam veteran, says Bush "really went over the line."

"I don't know how you can understand this, George, but that really hurts," McCain says.

The Swift Boat group also was being challenged by a Chicago Tribune editor who was on the Feb. 28, 1969, mission for which Kerry received the Silver Star. William Rood, 61, said he decided to break his silence about the mission because recent reports of Kerry's actions in that battle are incorrect and darken the reputations of veterans who served with Kerry.

"The critics have taken pains to say they're not trying to cast doubts on the merit of what others did, but their version of events has splashed doubt on all of us," Rood said in a 1,700-word first-person account published in Sunday's edition of the Tribune. "It's gotten harder and harder for those of us who were there to listen to accounts we know to be untrue, especially when they come from people who were not there."

Rood said the allegations that Kerry's accomplishments were overblown are untrue and that Kerry came up with an attack strategy that was praised by their superiors. According to the Tribune, Rood's recollection of what happened that day in South Vietnam was backed by military documents.

Rood wrote that Kerry recently contacted him and other crew members, requesting that they go public with their accounts of what happened.

"I can't pretend those calls (from Kerry) had no effect on me, but that is not why I am writing this," Rood said. "What matters most to me is that this is hurting crewmen who are not public figures and who deserved to be honored for what they did. My intent is to tell the story here and to never again talk publicly about it."

Kerry also picked up support from Wayne D. Langhofer, who told The Washington Post he was manning a machine gun in a boat behind Kerry's and saw firing from both banks of a river as Kerry dived in to rescue Special Forces soldier James Rassmann, the basis for Kerry's Bronze Star.

Until now, the Post noted on its Web site, Kerry's version of acting under fire had come from crewmen on his own boat. It quoted Langhofer as saying he was approached by leaders of Swift Boat Veterans for Truth several months ago but declined to join them in speaking against Kerry.

In Roanoke, Va., on Saturday, Democratic vice presidential candidate John Edwards also called on Bush to end the Swift Boat Veterans ads.

"This is a moment of truth for George W. Bush," Edwards said at a Democratic rally. "We're going to see what kind of man he is and what kind of leader he is. ... We want to hear three words: Stop these ads."