First, let’s be clear, Sanders will not win South Carolina. In fact, he will more than likely lose by a pretty large margin. According to Real Clear Politics, which averages all the polls, Clinton has a 28% lead in South Carolina. When looking at individual polls Clinton has closer to an 18 point lead. If you look back one month Sanders was down by as much as 40 points. He has clearly closed the gap. Sanders wins South Carolina, if he loses by less than 15%. If Sanders can do this it will show just how much he has closed the gap and if he can do that in the south you can expect him to win many less conservative states as the campaign moves on. Sanders indeed has an uphill battle, but he is in the same position Obama was 8 years ago.
Sources: Real Clear Politics