The effect of the Vietnam ads isn't likely to permanently damage Kerry or prove beneficial to Bush in the long term, analysts said.
"We've seen such a solid, intense vote out there that most stories, most events that occur in this campaign have only played around the edges," Goeas said.
Kerry's biggest challenge from the ads may be trying to shift the campaign back to issues that matter to undecided and independent voters, one Democratic operative said.
"The time he spends talking about this stuff, he's not talking about other things that swing voters care about," said Bill Carrick, a Democratic strategist who worked on Rep. Richard A. Gephardt's presidential campaign. "So you have a problem there."
The ads may have had their biggest impact with veterans, a majority of whom were already predisposed to vote Republican.
The third poll, which focused on veterans, shows that while Kerry made some gains with veterans after the convention, any improvement dissipated once the controversy over the ads erupted. It was conducted by the Annenberg Public Policy Center of the University of Pennsylvania.
The first commercial by the Swift Boat Veterans for Truth challenged Kerry's account of pulling a Green Beret officer out of the water after a mine explosion in the Mekong Delta of Vietnam. At issue is whether the Swift boats operating in that mission came under enemy fire.
The organizers of the ad campaign, some of whom were in boats on the river alongside Kerry that day, say they faced no weapons fire. Yet some Navy documents say at least one boat at the scene sustained bullet damage from enemy fire.
The veterans are now airing a new ad that focuses on Kerry's criticism of the Vietnam War once he returned to the United States, and his claims that U.S. policy led soldiers to commit atrocities.
The bipartisan Battleground poll of likely voters, conducted Aug. 15-17, has Kerry ahead with 49 percent and Bush with 47 percent. The Los Angeles Times poll of registered voters, conducted Aug. 21-24, has Bush ahead 49 percent to 46 percent, a reversal from a Times poll in July.
The Annenberg poll of veterans, conducted from Aug. 6-24, covered the period since the emergence of the Swift boat ads. Before the convention, 57 percent of veterans said Bush was a stronger leader than Kerry. Immediately after the convention, that number dropped to 43 percent for Bush, but the new poll has Bush back up to 56 percent.
The effect of the ads on Kerry was likely evident in his slippage on the question "Who has the honesty and integrity to serve as president?" Last month, Kerry and Bush tied on that question with 42 percent. This time, Bush has a decided edge at 46 percent to Kerry's 39.
Contact reporter James Kuhnhenn
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Ads critical of Kerry appear to be cutting into his support, new polls show. A2.