|Wednesday's debate in California turned into a fiery exchange between Romney, at left, and Perry, centre [AFP]
Republican presidential candidates have faced off in a debate over job creation, in the race to pick a challenger to President Barack Obama in next year's US elections.
Almost as soon as Wednesday's debate began in Simi Valley, California, Rick Perry, the Texas governor, and Mitt Romney, the former Massachusetts governor, challenged each other's record creating jobs.
Perry charged Romney with having one of the worst records creating jobs in Massachusetts in history, in an attempt to undermine Romney's argument that he can rebuild the US economy better than Obama.
"As a matter of fact, we created more jobs in the last three months in Texas than he [Romney] created in four years in Massachusetts," Perry said.
But Romney said Perry benefited from vast reserves of oil in a state that has no income tax, unlike Massachusetts.
"The reality is there are differences between states. I came into a state that was in real trouble ... I'm proud of what we were able to do in a tough situation."
Wednesday's 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 per cent and Obama's popularity is sinking in the polls.
Obama is to unveil a jobs plan on Thursday to try to bring down the high US unemployment rate, the main issue in the 2012 campaign.
The debate wandered across policy areas from homeland security to immigration, and foreign policy to welfare reform and climate change.
Perry risked to alienate millions of senior citizens by repeating attacks on Social Security, the government-run pension programme.
Perry declared the system a "Ponzi scheme", the kind of comment that Democrats can seize as proof that he would try to dismantle the government-run programme.
"It is a Ponzi scheme to tell our kids that are 25 or 30 years old today, you're paying into a programme that's going to be there. Anybody that's for the status quo is involved with a monstrous lie to our kids," he said.
It was up to Romney to defend the popular entitlement programme for seniors and allow him to appeal to independent voters who may well decide the 2012 election.
"You can't say that to tens of millions of Americans who live on Social Security and those who have lived on it," Romney said.
Al Jazeera's Rob Reynolds, reporting from Simi Valley, said Social Security was likely to become the major talking point in the wake of the debate.
"It's very popular and it's a very sensitive issue when any politician suggests tampering with social security," he said.
"The consequences are generally pretty dire. In this case, Governor Perry sounded an awful lot like he wanted to abolish the programme, calling it a monstrous lie, a Ponzy scheme etcetera".
The Perry-Romney exchanges largely overshadowed the six other candidates in the debate, reducing almost to spectators Michele Bachmann, the Minnesota congresswoman seen as the third-placed contender, and the other candidates.
Jason Johnson, a political analyst, told Al Jazeera that the Republican presidential competition had become a "two-man race" between the more conservative Perry and Romney.
"Everybody else looked like wallpaper," he said.
He said Perry was "not a very good debater" and described Romney's performance as "reasonable".
"It was his job to go into this and say 'this is a two-man race, between the extreme wing of the party and the moderate part of the party.
"But he didn't do a good job in establishing why people should pick a moderate instead of Rick Perry, who's a true believer".
Two polls this week put Perry in a strong lead: an NBC News/Wall Street Journal poll gave him 38 per cent against 23 per cent for Romney, while a Washington Post/ABC News poll put them on 27 per cent and 22 per cent.