Today, one of the most interesting political contests for the next few weeks will take place, and no one seems to know what the status of the race actually is.  Curtis Bostic squares off against former governor Mark Sanford in the runoff for the Republican nomination to represent South Carolina’s 1st Congressional District, a race that Bostic has tried to turn into a referendum on Sanford’s earlier scandal — as the two Republicans match up closely on most of the issues:

Sanford disappeared for five days while he was governor in 2009, telling his staff he was out hiking the Appalachian Trial. Later, he tearfully revealed at a Statehouse news conference he was in Argentina seeing a woman he later called his soul mate and to whom is now engaged.

Sanford, mentioned then as a possible presidential candidate, ended up divorcing his wife, Jenny.

Bostic says that behavior has left Sanford a compromised candidate who would give the Democrats a shot at taking back a district they have not held in more than three decades.

Sanford in turn has attacked Bostic for failing to turn in a financial disclosure form, including last night at a final “forum”:

Curtis Bostic attempted to use former Gov. Mark Sanford’s words against him in a debate Monday on the eve of the Republican runoff for the 1st Congressional District.

Sanford pushed back with criticism about Bostic’s failure to file a campaign-disclosure form.

The two squared off at a Hilton Head Island First Monday Republican Lunch Group forum — the last time the two men would debate before Tuesday’s runoff. It also was the only Beaufort County debate between the candidates.

Who’s poised to win today’s race and fight Elizabeth Colbert Busch in the special election to replace now-Senator Tim Scott? That’s a good question, since little polling has taken place in this primary, and none to my knowledge between the initial primary and today’s runoff.  Sanford scored an easy first place in the first primary, leading Bostic 37/13, but any anti-Sanford impulse would coalesce around Bostic rather easily.

The district seems safe enough that, contra Bostic, whoever prevails today should beat Colbert Busch.  As The State points out, Mitt Romney won this district by 18 points last November, although special elections such as these can produce big surprises, thanks to smaller turnouts and the resultant disproportionate impact of GOTV efforts.  We can bet that both national parties will sink a lot of money and effort into this race, simply because (a) a flip would provide all sorts of PR implications for both parties, and (b) nothing much else is going on until next month’s special US Senate race in Massachusetts.

What can we watch for in today’s race as it unfolds? Politico offers five keys to monitor, the first of which is the most important:

Turnout

No one thinks the contest will attract a swarm of voters. It is, after all, a special election runoff that comes two days after Easter. But how many people show up to the polls will say a lot.

A big turnout — say, 45,000 voters or more — is likely to benefit Sanford, who entered the runoff campaign with more than five times the amount of cash on hand as Bostic and who has far larger reach throughout the district. Sanford, who spent eight years as governor and six years in Congress, is so well known that one adviser estimated that nearly 80 percent of the Republican voters in the 1st Congressional District had supported him in one of his prior primary campaigns.

A low turnout, meanwhile, is likely to help Bostic, who has heavily geared his campaign toward a niche demographic of social conservatives. Bostic is betting that those supporters are highly motivated and will show up to vote no matter what.

A big turnout will also make the national party feel better about the upcoming general election.  Colbert Busch needs a small turnout to beat the Republican nominee no matter who it is, as the Cooke rating for this district is R+11.  They’d also like to see the “country clubbers,” in Politico’s parlance, turn out in order to gauge their enthusiasm for staying active throughout the process.  That should favor Sanford, especially since it appears that retirees went strong for Sanford in the first round.

Turnout will be the main key to watch.  If it gets too small, Bostic will probably drive it — but that has bad implications for the main event.