In about a half-hour, what’s called the “CNN-Southern Republican Debate” will get underway in Charleston, the 16th GOP debate of the cycle. It will be the first debate with only four candidates — Mitt Romney, Newt Gingrich, Rick Santorum, and Ron Paul — and it takes place just a couple of days before the South Carolina primary.

The good news, at least for us early-to-bed-early-to-rise types, is that the debate starts at 8 p.m. ET, rather than 9. The bad news is, it’s a two-hour event, rather than the usual 90 minutes.

It might also be the last debate with the full field for a while — the next debate is scheduled to take place shortly before the Florida primary, and Romney’s campaign has suggested he might not show up.

Tonight should prove to be pretty interesting. Romney has had a horrid week, and fears the primary is slipping away from him. He’ll not only be on the defensive over his tax returns tonight, but we might also see Romney taking a few shots at Gingrich. Indeed, in recent days, the former governor has become increasingly aggressive in his posture towards the former Speaker, and the more Romney attacks Gingrich instead of President Obama, the more it tells us about his internal polling.

It’ll also be interesting to see if Santorum aims for Gingrich, hoping to position himself as the main anti-Romney before it’s too late.

It’s pretty likely I’ll have some thoughts on the debate in the morning. In the meantime, the floor is yours.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.