Greenville, S.C. ? Howard Dean challenged John Kerry’s effectiveness as a senator Thursday night, contending that in 20 years, “not one” of the 11 health care bills introduced by the Democratic presidential front-runner had passed Congress.

Kerry retorted that he’d helped pass a lot — family medical leave, Agent Orange benefits for veterans and a new program of children’s health care that aids youngsters in Dean’s state of Vermont.

“One of the things you need to know as president is how things work in Congress if you want to get things done,” he said. He added that legislation written by one lawmaker often passes on a bill carrying the name of another.

The exchange, two-thirds of the way through a 90-minute debate, underscored the new order of the race for the Democratic presidential nomination.

Kerry walked onto the debate stage as the undisputed front-runner and logical target for his rivals after victories in the Iowa caucuses and New Hampshire primary in less than two weeks. That left Dean to play the role of aggressor as he tries to fix a candidacy in peril.

In all, 269 delegates will be at stake Tuesday in primaries in Missouri, Arizona, Delaware, Oklahoma and South Carolina, plus caucuses in North Dakota and New Mexico.

In the heart of Dixie, the Democrats insisted their party could compete successfully across the South against President Bush this fall, citing a loss of jobs, questions about postwar Iraq and administration trade policies as evidence.

“A president has to be able to walk and chew chewing gum at the same time,” said Sen. John Edwards, arguing that Bush has concentrated on the war on terrorism at the expense of domestic needs.

Edwards, Kerry and Dean called for an independent commission to investigate faulty prewar intelligence that Bush relied on in claiming that Saddam Hussein had weapons of mass destruction.

For some of the seven men on stage, the debate was possibly the last of the campaign. Edwards has said South Carolina’s primary was a must-win contest for him, and Sen. Joe Lieberman overrode the advice of advisers when he decided to remain in the race after a fifth-place New Hampshire finish.

Apart from Bill Clinton, Democratic presidential candidates have struggled mightily in the South in recent elections.

Democratic presidential hopefuls, from left, Sen. John Kerry, Sen. Joe Lieberman, Rev. Al Sharpton, Wesley Clark, Howard Dean, Rep. Dennis Kucinich and Sen. John Edwards stand together before a debate in Greenville, S.C. Thursday night's debate was the last before Tuesday's primary and caucuses in seven states.