By Wolf Blitzer, CNN

Charleston, South Carolina (CNN) – Here are a few things I will be looking for in Thursday night’s CNN Southern Republican Presidential Debate:

The four remaining candidates have been beating up on each other in recent days. Will they have the guts to blast their opponents when they are standing right next to them?

Rick Santorum, whom I interviewed Thursday in Charleston, has had an ad running that says Mitt Romney is “just like Obama.” He refers to Romney’s support for health care mandates in Massachusetts. Will Santorum look Romney in the eyes and repeat that line Thursday night?

Newt Gingrich told me in Iowa that he doesn’t think he could vote for Ron Paul if the Texas congressman were to win the GOP nomination. He cites Paul’s national security policies. Will Gingrich be prepared to go that far in the debate?

Is Romney going to announce that he’s ready to release his income tax returns now - as opposed to in April, as he suggested earlier this week? Even strong supporter New Jersey Gov. Chris Christie says he should be completely transparent.

Will the issue of Gingrich’s three marriages be a major issue? The reported comments by his second wife that he once wanted an “open marriage” have certainly generated a lot of commotion. Let’s see how the former House speaker handles that controversy and what his rivals say.

The many debates during this election cycle have been so important in this contest. Gingrich is surging in South Carolina now in part because of his strong performance in Monday night’s debate. Thursday night’s CNN debate will be must-see TV.

Tune in Thursday at 8 p.m. ET for the CNN/Southern Republican Presidential Debate hosted by John King and follow it on Twitter at #CNNDebate. For real-time coverage of the South Carolina primary, go to CNNPolitics.com or to the CNN apps or CNN mobile web site.

Follow Wolf Blitzer on Twitter: @WolfBlitzerCNN