Rivals for the Republican presidential nomination in 2012 have faced off in a debate at the Reagan Presidential Library in California.
Texas Governor Rick Perry, new to the debate cast, sparred with ex-Massachusetts Governor Mitt Romney over their records on job-creation.
Congresswoman Michele Bachmann reprised her belief that President Obama's healthcare policy was a "job-killer".
And Mr Perry called the US pension pot, Social Security, a "ponzi scheme".
As well as the three leading contenders, former Utah Governor Jon Huntsman, businessman Herman Cain, Congressman Ron Paul, former House of Representatives Speaker Newt Gingrich and ex-Pennsylvania Senator Rick Santorum also took part.
The debate is one of three scheduled in the coming weeks, and analysts say the Republican field is likely to thin out in the coming months. The 2012 primary season is not expected to begin until February.
Boisterous moments
Front-runners Mr Perry and Mr Romney dominated the early exchanges.
Mr Perry, a staunch conservative who immediately joined the leading group when he entered the race, boasts of his record of job-creation during 10 years as governor of Texas.
Mr Romney, who is selling himself on his private sector experience, unveiled his road map for the US economy on Tuesday.
Directly criticising his main rival, Mr Perry said he had "created more jobs in the last three months in Texas than he created in four years in Massachusetts".
Hitting back, Mr Romney said he worked as a Republican governor in a Democratic state, adding: "I'm proud of what we were able to do in a tough situation."
The discussion turned quickly to the topic of healthcare, with candidates unanimous in their repudiation of "Obamacare", the healthcare legislation passed by Congress in 2010 but bitterly opposed by Republicans.
Mrs Bachmann warned that the legislation would lead to "socialised medicine", while Mr Gingrich declared the bill a "monstrosity".
Both Mr Romney and Mr Perry insisted that, if elected, they would seek to repeal the law as soon as they took office in 2013.
The legislation, passed in 2010, extends health insurance to nearly all Americans, with new taxes imposed on the wealthy and restrictive insurance practices outlawed, such as refusing to cover people with pre-existing medical conditions.
On the defensive
The wide-ranging debate touched on topics as varied as fuel prices and homeland security.
Mr Perry was forced to defend his record as governor of Texas, and was singled out for his sceptical positions on climate change and evolution, and for passing a medical bill by executive order.
Under pressure, Mr Perry admitted he could "probably" have passed the legislation differently, adding he felt like a "pinata" being pummelled by his rivals.
The discussion was punctuated with occasional swipes at President Obama.
Mr Romney - who outlined a 59-point economic plan on Tuesday - commented that "the president's a nice guy, but he doesn't have a clue" how to get the country working. Mr Perry added that Mr Obama had "proven" he could not create jobs for America.
Mrs Bachmann - who took centre stage in the previous debate as she tussled with Minnesota Governor Tim Pawlenty - was less involved in the most boisterous moments.
Her brand of social and fiscal conservatism saw her win August's Iowa straw poll, considered to be an influential early indicator of possible leaders in the Republican presidential race.
But her campaign suffered a setback this week when campaign manager Ed Rollins and his deputy David Polyansky stepped down.
The other candidates sought to make their voices heard, with Jon Huntsman's appeal to a calmer, more centrist Republican tradition getting more of an airing than in previous debates.
The debate became part of a political spat when the White House announced a week ago that President Obama planned to deliver a joint address to Congress on the same night.
Amid Republican objections, the president was then forced to reschedule his address to Thursday night.
