Republican presidential rivals Rick Perry and Mitt Romney tangled over their records on creating jobs in a campaign debate that marked a contentious new turn in the race to pick a challenger to President Barack Obama next year.
The debate was the first of three in as many weeks, at a time when the economy is struggling, unemployment is seemingly stuck at 9.1% and Mr Obama's popularity is sinking in the polls - all making the president seem more vulnerable than he appeared only a few months ago.
Far more than in earlier debates this summer, the candidates mixed it up in their first face-off since Mr Perry, the Texas governor, entered the race and almost instantly overtook Mr Romney, the former Massachusetts governor, as front-runner in opinion polls.
Those two - as well as the six other contenders on stage - sniped at one another, contradicted allegations and interrupted questions from moderators to demand opportunities to take on each other.
Almost as soon as the debate began, Mr Perry and Mr Romney challenged each others' record creating jobs.
Mr Perry said that Michael Dukakis, a liberal predecessor of Mr Romney and former presidential candidate who is widely disparaged by Republicans, created jobs more quickly than Mr Romney.
Mr Romney responded that Mr Perry's predecessors in Texas - including former President George W. Bush - created jobs more rapidly than Mr Perry had.
Mr Perry's front-runner status was clear from the barbs he took from other candidates. "I kind of feel like the pinata here at the party," he joked.
Without naming Mr Perry, former Utah Governor Jon Huntsman challenged the Texas governor's scepticism on climate change and evolution.
"In order for the Republican Party to win, we can't run from science," said Mr Huntsman, Mr Obama's former ambassador to China who is running near the bottom of opinion polls.
But Mr Perry defended his views on climate change: "The idea that we would put Americans' economy in jeopardy based on scientific theory that's not settled yet to me is just - is nonsense," he said.
Mr Perry also defended the death penalty in Texas, where 234 people have been executed during his tenure as governor.
He said he's never struggled with whether any of the inmates executed might have been innocent. His comments drew strong applause from the audience.
Mr Perry and Mr Romney stood next to each other on the debate stage at the Ronald Reagan Presidential Library, a symbolic setting that invoked the memory of the conservative Republican who swept to two terms as president.
The debate came one day before Mr Obama delivers a major address on creating jobs before a joint session of Congress. The Republican contenders had little positive to say about Mr Obama, either his record on creating jobs or his signature health care law, which they have vowed to repeal if they win the White House.
But Mr Perry volunteered praise for Mr Obama's order that resulted in the death of Osama bin Laden in a US military raid in Pakistan, and saying he was happy the US prison at Guantanamo has been kept open.
Mr Perry and other candidates went after Mr Romney over his health care plan in Massachusetts, which required residents to purchase insurance. That requirement in Mr Obama's health care plan is one of its most controversial provisions.
Mr Romney, meanwhile, criticised Mr Perry for denouncing the Social Security pension programme for the elderly. Mr Perry called Social Security "a monstrous lie" and said young people will never receive the benefits they had been promised.
Mr Perry, who cut short his campaign appearances this week to deal with wildfires raging in Texas, flew to California for the debate even though the flames were not extinguished.
It was his first national debate appearance. Mr Romney ran for president in 2008 and has honed his debate skills since then.
The debates are important for Michele Bachmann, the Minnesota congresswoman looking look to keep her name near the top of a pile that also includes former House of Representatives Speaker Newt Gingrich, former Pennsylvania Senator Rick Santorum, businessman Herman Cain, Texas Representative Ron Paul.
Ms Bachmann's standing rose quickly this summer, and she won a key test vote in Iowa on August 13. But Mr Perry's entrance into the race eclipsed her, and she has seen staff upheaval this week, losing her campaign manager and her deputy campaign manager.
Former Alaska Governor Sarah Palin, the Republican vice presidential candidate in 2008, has not yet announced if she will enter the race.