The first and only debate between Mark Sanford and Elizabeth Colbert Busch in South Carolina's 1st district special election campaign is happening tonight. Given how wildly unpredictable the race has been so far, it's not to be missed.

We'll have complete coverage over on Post Politics this evening of the set-to sponsored by the Patch news service, the South Carolina Radio Network, and Charleston 's WCBD-TV. In the meantime, here are the five things to watch for tonight beginning at 7 p.m. ET:

1. Can Sanford shift the momentum? A draw in tonight's debate may as well be counted as a win for Colbert Busch. The Democrat has seized the high ground in this race during the last couple of weeks, and with eight days left, if Sanford is going to spring a comeback, he could use a big moment (or several) in the debate. What Sanford needs is a Colbert Busch misstep, a commanding performance of his own, or both. After a downright disastrous period of bad press that began with the revelation that Sanford's ex-wife accused him of trespassing on her property, the former governor needs to turn the page. There's no better opportunity than tonight to do it.

2. How will Colbert Busch perform on the big stage? Sanford's a debate veteran while Colbert Busch is a political newcomer who has never participated in an event as big as this one. This will be her toughest test yet. A big part of winning campaigns is making voters feel comfortable with who you are. How Colbert Busch comes across will be as important as what she says.

3. Keeping it national: Sanford's campaign has consistently hit Colbert Busch by trying to tie her to national Democrats and slamming her for taking union money. We can reasonably expect Sanford to ask Colbert Busch where she agrees and disagrees with the national party, given the heavy Republican tilt of this district. Something else to keep an eye on: A pool of deleted tweets from Colbert Busch that could be a target of criticism from Sanford.

4. Keeping it local: On the other hand, the Democratic attack pattern against Sanford has consistently centered on his record as South Carolina governor, including the ethics fine he paid, and less directly, his disappearance from the state in 2009 to visit his then-mistress and now fiance. Colbert Busch is in a strong position, so she doesn't have to be in full attack mode tonight. It will be interesting to see if the Democrat goes after Sanford on any of these fronts, or stays positive and leaves it to the Democratic outside groups that have served as the attack dogs over the airwaves.

5. Surprises: It's the unexpected stuff that usually grabs headlines coming out of debates. And given the many twists and turns we've already seen in this race, a surprise development tonight wouldn't be, well, surprising (see what we did there?). An unexpected stumble or gaffe, and surprise line of attack, an especially heated moment -- these are the the things that could upstage everything else.