(Updated February 17th to include post-debate data. The conclusions are unchanged.)
The Republican primary in South Carolina is this Saturday, February 20th. Donald Trump continues to lead the pack, with
36 percent support in four post-N.H. surveys 34 percent support in two surveys done after last Saturday’s debate. His closest competitor is Ted Cruz, Marco Rubio, or John Kasich, depending on the survey. Trump’s median lead over the second-place finisher is 18.5 17 percentage points.
South Carolina’s Republican convention delegates are assigned on a winner-take-all basis, either at the state level (29 delegates) or by Congressional district (21 delegates in 7 districts, 3 delegates each). As a general rule, Congressional districts within a state behave similarly in a primary. Consistent with this, in 2012 Congressional Districts 2 through 7 showed an average margin of 14.7% between the first-place candidate (Newt Gingrich) and the second-place candidate (Mitt Romney), with a standard deviation of only 5.1%. The outlier was District 1, which includes Charleston, and which Romney won by a 2.9% margin.
District 1 is probably biased toward the less-evangelical candidate (such as Romney in 2012). In this year’s field, Trump, Kasich, and Bush should split the non-evangelical vote, and so District 1 might not differ that much from the six other districts. It is distinctly possible that Trump will win all seven districts – and all 50 of South Carolina’s convention delegates. That would bring Trump to a total of 67 out of 103 delegates awarded so far, or 65%.
After South Carolina, Nevada votes on February 23rd. Nevada awards its 30 delegates with genuine proportionality, so Trump should get about 10 delegates there. That would put him at 58% of delegates heading into Super Tuesday.
On the same day as the GOP primary in South Carolina, Democrats vote in Nevada. However, it’s a hard state to poll and so there is no good data. Looking ahead, the Democratic primary in South Carolina is on February 27th. In five recent polls taken since the New Hampshire primary, Hillary Clinton leads Bernie Sanders by a median of 19 percentage points. If this holds up, she would win with close to 60 percent of the vote. Like most Democratic primaries, South Carolina’s delegates are awarded proportionally, not counting superdelegates. So she should make up all the ground lost in New Hampshire, plus a few extra delegates.