There’s a long list of House seats flipping in the wake of scandal: Anthony Weiner saw his Queens district flip to Republicans in the wake of his sex scandal. One month after winning a Republican primary in March 2006, an indicted Tom DeLay opted not to run for re-election, recognizing there was a good chance he’d lose despite representing one of the most Republican seats in the country. That same year, Rep. Don Sherwood couldn’t overcome the blowback from news that he choked his mistress, coughing up his ruby-red district in northeast Pennsylvania. All those seats were considered safely in one party’s corner, until scandal struck.

Second, special elections are notoriously unpredictable. Democrats won several seats in the heart of the Deep South in 2008 off-year elections, and Republicans picked up a seat in Hawaii just before the 2010 midterms. Like all special elections, the race will turn on which side can generate more enthusiasm from the base. Given Sanford’s high unfavorable ratings, it’s very possible a lot of Republicans will choose to stay home, giving Democrats an opportunity to win the turnout battle.

Third, even though the race is taking place in South Carolina, the Charleston-based district favors country club Republicans over social conservatives. That could play to Sanford’s advantage — these voters may be more forgiving of his sins — but it also suggests they’d be more receptive to voting for a moderate Democrat than their more evangelical counterparts in the western part of the state. The district nearly elected an openly-gay businesswoman, Linda Ketner, who took 48% of the vote in 2008 against then-Republican congressman Henry Brown.