A head to head comparison of the South Carolina 2012 General Election gives us an idea of the break down of the voters.    

Mitt Romney received 1,049,510 (55%) votes, beating Barack Obama who gained 845,756 (45%) by 203,754 votes in South Carolina.

Mitt Romney won 25 counties whereas Barack Obama won 21 counties in the total of the 46 counties in the State of South Carolina.

Presidential General Elections

During the 2012 General elections, over 122M total number of votes were cast. Barack Obama got 62,614,654 (62.6 Million) over Mitt Romney's 59,141,654 (59.1 Million). He won the popular vote by 3,472,979 (3.4 Million). Even though he lost to Mitt Romney in the State of South Carolina, his 845,756 gained votes represents 1.3% of his popular vote victory. The remaining 49 states contributed to the remaining 98.7% popular votes victory.

Top 15 Counties in Primary Elections vs General Elections

All Candidates (General Elections)

These 15 counties play an important role in these Primary elections. If a candidate, can get a sizable majority in the larger counties (Greenville, Charleston, Richland, Lexington, Spartanburg, Horry), it becomes very difficult to win majorities in the smaller counties without voter outreach and increased voter participation in them.

Top 15 Counties Comparison in Primary Elections vs General Elections

General Elections
Barack Obama

General Elections
Mitt Romney

Richland and Charleston, two of the larger counties, voted in favor of Barack Obama giving him a 51k vote advantage. Greenville, Lexington, Spartanburg and Horry, some other larger counties voted in favor of Mitt Romney giving him a 150k voter advantage in those counties. However, Romney's steady win in the less dense counties was enough to maintain that difference, making him gain an upper hand in the State of South Carolina.

Related References: 2016 South Carolina Primary Election Story, 2016 South Carolina General Election Story, 2020 South Carolina Primary Election Story, 2020 South Carolina General Election Story