A newly trimmed field of five Republican presidential hopefuls meets tonight in a South Carolina debate that gives front-runner Mitt Romney's rivals one of their final chances to derail his growing momentum.
The debate comes hours after former Utah governor Jon Huntsman dropped out of the 2012 Republican race and endorsed Mr Romney, bolstering the former Massachusetts governor's drive for his party's nomination. Mr Romney won the first two state nominating contests in Iowa and New Hampshire this month.
It also provides Rick Santorum and Newt Gingrich a prominent stage for their battle to become the top conservative alternative to the more moderate Mr Romney.
Mr Santorum, a former US senator from Pennsylvania, gained valuable backing in that effort over the weekend when a group of 150 religious and social conservative leaders agreed to coalesce behind his candidacy in an effort to stop Mr Romney.
The debate is the first of two this week in South Carolina, where a Romney win in Saturday's primary could put him on an almost certain path to clinching the right to challenge president Barack Obama in November's election.
Polls show Mr Romney with a solid lead in South Carolina over Gingrich, the former US House of Representatives speaker, heading into the debate. Another debate will be held in Charleston on Thursday, less than 48 hours before South Carolina Republicans start to vote.
Mr Romney, Mr Gingrich, Mr Santorum, Texas governor Rick Perry and US Representative Ron Paul will meet in the two-hour debate at 9pm EST (0200 GMT on Tuesday) in Myrtle Beach, South Carolina.
The last Republican debates were back-to-back meetings within 12 hours of each other before the New Hampshire primary, which Mr Romney won easily after narrowly winning in Iowa.
Those debates featured several sharp attacks on Mr Romney for his work at a private equity group that critics say plundered companies and slashed jobs, but his Republican rivals have eased off those criticisms in recent days.
South Carolina's unemployment rate is higher than the national average of 8.5 per cent, making jobs and unemployment one of the most prominent topics expected to be tackled in the debate.
Mr Santorum, Mr Gingrich and Mr Perry have pursued South Carolina's large bloc of evangelical and social conservative voters, who have been split here, as they were in Iowa.
Mr Santorum, who came in second in Iowa, and Mr Gingrich have argued they are the most electable conservatives, but neither have shown signs in polls yet that they are breaking through in South Carolina, which could be the last chance to stop Romney.
The next battleground after South Carolina will be Florida on January 31st, a huge and diverse state where Mr Romney's financial and organizational advantages would make him hard to stop.