Republican presidential contenders have turned the heat on the two frontrunners in a debate, attacking businessman Herman Cain's economic plan as a tax increase and former Massachusetts Governor Mitt Romney over his health care law.
Michele Bachmann led the assault in Las Vegas, saying Mr Cain's call for a 9% federal sales tax would only be the beginning, with the rate rising later.
Former senator Rick Santorum cited one analysis that found that taxes would go up for 84% of American households under the plan.
Texas Governor Rick Perry and Mr Santorum took Mr Romney to task over Massachusetts' health care law that Democrats used as a model for their national health care plan.
Mr Perry said Mr Romney is being dishonest about his record on the law, while Mr Santorum was more direct: "You just don't have credibility, Mitt." Mr Romney defended his plan as right for his state but wrong for the nation.
Mr Cain, for his part, insisted the charges about his tax plan were untrue and that he was being criticised because lobbyists, accountants and others stood to benefit from the current tax code.
Mr Cain has never held public office, but has built up a following among conservative activists as a radio talk show host and motivational speaker. That background has boosted his popularity with his poll numbers having jumped to put him in a dead heat with the presumed front-runner, Mr Romney.
All are vying for the Republican nomination to challenge Democratic President Barack Obama in 2012, and many undecided voters have been watching the debates to evaluate the candidates.
Much of the focus has been on Mr Cain's catchy 9-9-9 tax overhaul plan which he has made the centrepiece of his campaign. The plan would scrap the current tax code and replace it with a 9% tax on personal income and corporations as well as a new 9% national sales tax.
Ron Paul and former House of Representatives Speaker Newt Gingrich also took part in the debate, the fifth in six weeks, and the last scheduled for nearly a month in a race that is fluid in more than one way. While polls chart a series of rises and falls for various contenders - Mr Romney remaining at or near the top - the schedule is far from set.