Republican presidential contenders have taken part in a televised debate in Arizona, days before two states hold significant primary elections.
Rick Santorum came under attack from his rivals over his voting record when he was a senator, including earmark spending and voting to raise the debt ceiling.
This is the last time the candidates will appear together ahead of Super Tuesday, when ten states vote.
This was a crucial debate for Mr Santorum, the conservative former senator from Pennsylvania, who has been rising in the polls.
An aggressive Mitt Romney repeatedly put Mr Santorum on the defensive and attacked the former senator and staunch social conservative for supporting big-spending government programmes.
Mr Santorum's sometimes awkward defence of votes he cast in the Senate, including his claim that politics was a "team sport" and that he sometimes had to vote for bills that did not like, could hurt his support among conservatives tired of Washington politics-as-usual.
Mr Romney had a better debate compared to his recent performances and succeeded in painting his main opponents as political insiders, while he is the competent outsider, steeped in the business world.
The debate was at times petulant and angry and combative with the only moments of distraction and lightness provided by the outsider libertarian, Ron Paul.
Former Speaker of the House Newt Gingrich is hoping to rebound from his recent drop in the polls to reassert himself during some of the March contests in Southern states like Georgia, Oklahoma, Mississippi, Alabama and Louisiana.
Two contests will be decided in the next week before Super Tuesday in early March, which will be the defining day of the campaign.
Review of US corporation tax
Meanwhile, the Obama administration has proposed a full review of US corporation tax rates.
It suggests that the headline rate should be brought down from 35% to 28% in general and to around 25% for manufacturing.
The proposals have been sent to the budget sub-committees in Congress and will be discussed there before any legislative proposals are produced.
President Barack Obama and Treasury Secretary Tim Geithner are proposing a wide ranging review of the complicated US corporate tax system.
At its heart is an attempt to simplify that system and to reduce the headline rate of corporation tax, which, at 35% is one of the highest in the developed world.
But there are other proposals that might impinge on Ireland's position as a big recipient of US investment.
The President is proposing an end to a tax break that allows US companies to get a tax credit for any investment overseas.
President Obama is also proposing to impose a minimum tax on overseas profits so as to prevent US companies from reaping the benefits of locating profits in low-tax countries.
There is no surprise that this is being produced in an election year and even less surprise that the proposals will be subject to the usual tortuous round of lobbying and partisan bickering in Congress.
The report is a joint report by the White House and the Treasury Department.
It has been known for some time that senior Democrats have been uneasy with the rate of corporation tax and with what they regard as the 'over-generous' treatment of foreign profits earned by US companies.
The aim of the proposals is to maximise the investment, growth and job potential of US companies in the US.
Ireland is not mentioned as one of the countries that have a high amount of US company profits relative to their GDP, or size of economy, but it is one of the biggest recipients of foreign direct investment by US companies in the world.
