When will South Carolina become a swing state?

[Vosem]

South Carolina is...not trending Democratic? Here're presidential margins, and leans compared to the nation:

2016: Trump+14 (R+16)
2012: Romney+11 (R+15)
2008: McCain+9 (R+16)
2004: Bush+17 (R+14)
2000: Bush+16 (R+16)

No particular trend in any direction in the 21st century. Sure, 2018 was a pretty decent year for the South Carolina Democratic Party, but I think that's mostly explicable by 2018 being a pretty good year for the Democratic Party in general. Here're South Carolina House margins and leans compared to the nation for the 2010s (this is quick-and-dirty done by averaging margins between districts, so it doesn't take into account differential turnout -- on a national scale it should overstate Hispanics at the expense of white liberals, but in SC it shouldn't matter much at all since both groups are scarce):

2018: Republicans+9 (R+17)
2016: Republicans+18 (R+17)
2014: Republicans+35 (R+30) **Ds did not contest SC-1[1] or SC-4
2012: Republicans+17 (R+18) **both parties left 1 seat uncontested
2010: Republicans+15 (R+8)
2008: Republicans+1 (R+11)
2006: Republicans+11 (R+19)
2004: Republicans+33 (R+31) **Ds did not contest SC-1 or SC-3
2002: Republicans+21 (R+16) **Ds did not contest SC-1 or SC-2; Rs did not contest SC-5
2000: Republicans+15 (R+14) **Ds did not contest SC-4

[1] Yes, the seat Joe Cunningham flipped was not contested in 2014, even though at a 2013 special election Democrats had already held the margin to single digits.

It's possible to get better numbers by estimating results for the uncontested seats using data from the races where the race was contested and applying national swings, but you basically get the picture. There doesn't seem to be a coherent trend in any direction in South Carolina; John Spratt retiring but Democrats leaving seats uncontested less often basically cancelled each other out.