Taxes, trade and foreign policy were all up for discussion in Johnston on Sunday, 10 months before American voters will choose who gains the keys to 1600 Pennsylvania Avenue.
Democratic hopefuls took aim at front-runner Howard Dean, with Joseph Lieberman, John Kerry and Richard Gephardt leading the attack against the former Vermont governor.
Lieberman, a Connecticut senator who earlier in the day said Dean had "a short fuse and quite a temper," slammed his comment that the capture of Saddam Hussein in Iraq had not made America safer.
Kerry, a Massachusetts senator, criticised Dean for a recent remark that he would not prejudge the guilt of al-Qaida leader Usama bin Ladin.
With the race intensifying, they said a series of recent controversial statements by Dean showed he did not have the temperament or judgement to lead the party in a general election race against US President George Bush in November.
Kerry told Dean the statements raised "a serious question about your ability to be able to stand up to George Bush and make Americans feel safe and secure."
Dean defended the bin Ladin comment, saying as president he would have to uphold the rule of law and said recent events such as the raised US alert level had shown his comments about former Iraqi president Saddam Hussein were right.
"The fact is, since Saddam Hussein has been caught, we've lost 23 additional troops; we now have, for the first time, American fighter jets escorting commercial airliners through American airspace," Dean said.
Missouri congressman Gephardt criticised Dean on trade for supporting revisions to the North American Free Trade Agreement to include more labour and environmental standards, but backing the treaty when it was passed.
Gephardt said the pact had led to a job drain in the United States. "It's one thing to talk the talk, it's another thing to walk the walk, we've got to get labour and environment in these treaties."
"The fact is, since Saddam Hussein has been caught, we've lost 23 additional troops; we now have, for the first time, American fighter jets escorting commercial airliners through American airspace"
Democratic presidential contender
The debate kicked off an intense two-week race to the caucuses in Iowa on 19 January, with New Hampshire voting in the nation's first key primary the week after.
After the Iowa and New Hampshire contests in January, the nominating process moves to seven more states on 3 February, when each contender hopes to emerge as a clear alternative to Dean and rally the more moderate elements of the party.
Dean's fiery denunciations of Bush, the Iraq war and Democratic leaders in Washington have taken him to the top of the pack, but raised questions about whether he can expand his support in a contest against Bush.
Refusing to be drawn into a lengthy debate with his rival party contenders, Dean said Washington Democrats like Lieberman, Kerry and Gephardt had failed to mount a challenge to Bush and he would draw new supporters to the polls.
"What has happened to so many Democrats in Congress is that they've been co-opted by the agenda of George Bush, who came into office with 500,000 fewer votes than Al Gore … what we need is a Democrat who's going to stand up to George Bush," he said.