The biggest challenges for Gingrich, however, are Santorum and Perry, who are taking almost one-third of the vote in the new CNN/Time/ORC poll. Gingrich is unabashedly and publicly urging conservatives to get behind him, suggesting that voting for either of the other two would only boost Romney because neither of them can win.
Santorum has called Gingrich's suggestion "arrogant," pointing to his No. 2 finish in the Iowa caucuses, where he lost to Romney by eight votes, and his tie with Gingrich in the New Hampshire primary.
"It is an enormous amount of hubris for someone who lost their first two races," to imply that he should be the presumptive choice for conservatives, Santorum said of Gingrich Tuesday.
All four candidates were out on the campaign trail courting South Carolinians. One candidate that was notably absent from the Palmetto State today, however, was Ron Paul. The congressman from Texas, who was booed in Monday night's debate on his foreign policy answers, has taken a break from the campaign trail and is in Washington, D.C.. to vote for a bill against raising the debt ceiling to $1.2 trillion, as the president has requested.
The South Carolina primary is a crucial test for Republican candidates. Every candidate since 1980 who has won that state has gone on to win his party's nomination. It is also an important bellwether of how other southern states will lean in their caucuses and primaries.
ABC News' Elicia Dover and Emily Friedman contributed to this report.