South Carolina has always permitted fusion (i.e., letting two parties jointly nominate the same candidate), but it has not been used very much in the last 100 years. The Working Families Party, which has been ballot-qualified in South Carolina starting in 2006, had had to struggle to persuade Democrats (those that the party wants to cross-endorse) to accept the WFP nomination.
This year, however, four Democratic nominees for U.S. House are also Working Families Party nominees. By contrast, there were only two such U.S. House Democratic nominees who accepted the party’s nomination in 2006, and none in 2008, and one in 2010. Of course, sometimes the Working Families Party does not desire to nominate certain Democratic nominees.
Here is an article about the Working Families Party’s four nominees for U.S. House. The Working Families Party also has more legislative nominees (again, they are also Democratic nominees) than ever before in South Carolina.
South Carolina, like New York and Connecticut, lets the voter choose the party label for candidates who are the nominees of two parties. So, a voter can not only vote for such a person, but can choose whether to cast the vote under the Democratic label or the Working Families label. Most states that permit fusion do not give the voter that option.