Stephen Colbert may have opted not to pursue a serious political campaign, but another Colbert, his sister, is embarking on one of her own. And though it's still too soon to predict the final outcome, early signs indicate that she has a surprisingly good chance of pulling off a huge upset and capturing what was once a solidly Republican seat.

On Tuesday, a Public Policy Polling survey showed Democrat Elizabeth Colbert Busch in a virtual tie with likely challenger Mark Sanford in the special election to fill South Carolina's vacant House seat. Busch led Sanford 47 percent to 45 percent, just within the poll's 2.9 percent margin of error.

The poll also found Busch tied, at 43 percent, with Curtis Bostic, her other potential foe for the May special election. Bostic and Sanford will go head-to-head in a Republican primary run-off next week, a contest Sanford is heavily favored to win, despite having left the governor's office in disgrace after his bizarre extramarital affair came to light four years ago.

That Busch is performing so well may come as a bit of a surprise. The seat in question, representing South Carolina's 1st District, is reliably red. It hasn't been held by a Democrat in more than 30 years, and Tim Scott (R) last November won re-election there with 62 percent of the vote — double what his Democratic challenger received. (In December, South Carolina Governor Nikki Haley (R) appointed Scott to fill a vacant Senate seat, prompting the special election.)

So why is Busch performing so well?

Voters still haven't forgiven Sanford. The former governor, who is seeking to reclaim the House seat he held in the late 1990s, snuck out of the state in June 2009 to visit his Argentinean mistress. His office initially said he was hiking the Appalachian Trail, though as more details came to light, Sanford admitted to the affair and became a national punchline, his popularity cratering in the process.

"Focusing in on the potential race between Busch and Sanford, it's surprisingly close for one simple reason — voters like Busch and they continue to strongly dislike Sanford," PPP's Tom Jensen wrote in announcing the poll's results.

While 45 percent of respondents in the poll had a favorable opinion of Busch, only 34 percent said the same of Sanford. Worse for Sanford, a 58 percent majority said they had an unfavorable opinion of him.

Sanford is so unpopular, even conservatives are openly criticizing his credentials and integrity. "Leave it to Republicans to mess up a South Carolina House seat," The Washington Post's Jennifer Rubin lamented.

Busch is also being buoyed by some Democratic star power. Stephen Colbert campaigned for her this year — in a rare out-of-character appearance, no less — while Vice President Joe Biden and Maryland Gov. Martin O'Malley, both of whom are believed to be eyeing a 2016 White House bid, praised her on unrelated visits to the state.

And Busch can pull her own weight. As a top official with Clemson's business school, she's relatively well-known in the state and has a reputation as a business-savvy centrist. That centrist appeal is key, since it has helped her draw crucial support across the aisle. As MSNBC's Ali Weinberg noted, at least 16 of Busch's donors recently made contributions to Republican candidates as well.

Still, given the district's strong Republican leaning, Busch remains an underdog in the race. There's still a large crowd of undecided voters, a group that, in PPP's poll, backed Romney by a 77 percent to 12 percent margin last November. As Jensen notes, that bloc could coalesce behind whichever Republican candidate wins next week's run-off, tipping the odds against Busch.

With two months to go, though, Busch appears poised to at least make the race interesting. If Sanford wins the primary, Busch would have an even better chance of making the GOP's fears of squandering a safe seat a reality.