Democrat John Kerry (search) accused presidential rival Howard Dean (search) of lacking principles and flip-flopping on key issues Thursday, hoping to convert the front-runner's fumble over the Confederate flag (search) into a sweeping indictment of Dean's policies and personality.

"I think Americans deserve straight talk. I think they ought to know who Howard Dean is," the Massachusetts senator said.

The Dean campaign immediately shot back.

Dean's spokeswoman said Americans deserve to know why Kerry has struggled to explain his support for President Bush's Iraq war resolution. "It's become increasingly clear that John Kerry is a heck of a lot better at formulating negative attacks than formulating a straightforward position on Iraq," said Tricia Enright.

Kerry opened the broad line of attack a day after Dean belatedly apologized for urging Democrats to court Southern whites who display Confederate flags in their pickup trucks. The flap gave hope to Kerry and seven other candidates trailing Dean in this key early primary state.

Their challenge intensified Thursday as the 1.6 million-member Service Employees International Union threw its support behind Dean. A second AFL-CIO powerhouse, the American Federation of State, County and Municipal Employees, planned to join the SEIU in a rare joint endorsement next week.

A new American Research Group poll showed Dean with a 14-point lead over Kerry in New Hampshire, a state both New Englanders must win.

Flanked by state law enforcement officials, Kerry pointed out that Dean mentioned the Confederate flag in defense of his policies on guns. Dean regularly argues that his record as Vermont's governor -- endorsed by the National Rifle Association -- will help him court Southern white males who oppose gun control.

"Howard Dean has said he's against a ban on assault weapons, a background check for criminal records, and even a short waiting period for buying a gun," Kerry said. "In falling in line with the most extreme elements of the NRA, Howard Dean didn't offer straight talk, he offered straight-up pander to one of the most powerful special interest groups in America."

Dean now says he supports the ban as well as closing the gun-show loophole that allows purchases of weapons without background checks. Beyond that, Dean has said states should be allowed to go their own way.

Kerry said Dean's shift on gun policy fits a pattern in which the former governor has changed his views on a number of issues since the 1990s, including Social Security, Medicare, trade and public financing of elections. Dean held relatively moderate views as governor, and now is more in line with traditional Democrats who vote in the primaries.

"It's not enough just to switch your positions in the presidential race," Kerry said. "These are issues of principle."

On one of those issues, however, Dean and Kerry are carbon copies. Both candidates have long claimed to support public financing of elections, but now Dean is poised to opt out of the federal system and Kerry said he may follow suit.

"If he gets out, he invites somebody else to get out," Kerry said.

Their justification is strikingly similar: The senator says he may opt out because he fears Dean will outspend him in the primaries; Dean says he may get out because he fears Bush will outspend him in the general election.

Said Enright: "To quote John Kerry's favorite philosopher, Yogi Berra, I guess when John Kerry came to the fork in the low road, he took it."

While Dean and Kerry fought for the front-runner's mantle in New Hampshire, other candidates viewed the Confederate flag flap as an opportunity to move into the top tier.

John Edwards, campaigning in New Hampshire much of the week, drew praise from several Democratic voters for condemning Dean's remarks in Tuesday night's debate. Some said it was a breakout moment for the North Carolina senator who has had trouble gaining ground in the state.

Dean's rivals said the controversy underscored personality traits that could haunt the front-runner, starting with his stubborn refusal to apologize during the debate.

Dean himself acknowledged the flaw. "You know how I am, if somebody comes at me, my tendency is to go right back at them and worry about it later," he told reporters.