As we await the results from today's voting in South Carolina, it's worth revisiting some lessons from the last three contested Republican primaries in South Carolina.
To start with, as I noted yesterday, turnout has been wildly variable in past South Carolina GOP primaries, and the state has been so decisive in part because every winner except John McCain in 2008 has won by a double digit margin of victory:
A few things to watch from past primaries:
Independents and Democrats were just 20% of the 2008 primary electorate (18% independents, 2% Democrats), compared to 29% (25% independents, 4% Democrats) with no Democratic primary going in 2012 and a whopping 39% (30% independents, 9% Democrats) in 2000. They were decisive in 2008, as Mike Huckabee narrowly won Republicans 32-31 over John McCain but lost independents 40-26 to McCain. McCain in 2000 beat Bush by more than 50 points with Democrats and 25 with independents, but still got swamped by Bush's advantage with Republicans (he got 68% of South Carolina Republicans). In 2012, Newt Gingrich and Mitt Romney both ran stronger among Republicans (45-28 Newt over Mitt) than among independents (31-25), because Ron Paul won 23% of independents but only 10% of Republicans. The Paul voters are a segment to watch today, as they seem likely to mostly back Trump, except that the more traditionally libertarian ones may break for Ted Cruz.
In any event, independents are likely to be a smaller proportion of the vote here than in New Hampshire, where they routinely crack 40% and were 44% this year. If we see numbers that high here, it's great news for Trump and Kasich.
Newt in 2012 won every age group but under-30, who were won by Paul. Those voters were just 9% of the vote. Watch that age bracket (now the under-35 vote) today. In 2008, they were 10%, and voters 18-44 went for Huckabee, 45-up went for McCain. My guess would be that the McCain 00/08 voters included a lot of older veterans who have died or otherwise dropped out of the electorate by now. In 2008 - exits didn't ask this in 2012 - 21% of SC primary voters were veterans, and 55% were born outside SC (a figure roughly consistent with the population).
In a lot of states, the Republican primary electorate is heavily male. Not so in South Carolina, where the big partisan fault lines are racial rather than gender; in both 2012 and 2008, the voters were 51/49 male.
Here's the #1 issue in the exit polls:
2008: Economy 40, Immigration 26, Iraq 16, Terrorism 15
2012: Economy 63, Deficit 22, Abortion 8, Immigration 3
You could say that's a dramatic shift. But the outcomes are not always predictable: in 2008, John McCain of all people won 26% of SC primary voters who said we should deport all illegal immigrants. And being out of power changes voter priorities: electability was the top candidate characteristic for just 6% of GOP SC primary voters in 2008, but 45% in 2012. Yet voter perceptions are not always those of the media or party elites: of those "electability" voters in 2012, 51|% voted for Newt Gingrich.
Religious conservatives were decisive for Bush in 2000, as what the media then called "white Religious Right voters" went for Bush 57-38 and were about a third of the vote. Evangelical or Born-Again Christians were 60% of the vote in 2008, 65% in 2012 with higher turnout. Numbers that large would bode well for Cruz in particular; it's almost triple their share of New Hampshire 2016 and more in line with Iowa 2016.
Catholics may not be numerous in SC (~7% of population) but they're overrepresented in GOP primary: 13% in both 2008 & 2012, a number that may not bode real well for Donald Trump on the heels of his spat with the Pope. And look at this breakdown for Romney in 2012:
Voters making under $50k a year were 28% of the SC GOP primary electorate in 2008, 36% in 2012. It's debatable how much that reflects shifts in the economy versus shifts in who voted (almost a third of 2012 voters said someone in their household had been laid off the prior three years), but these have tended to be more pro-Trump voters in the early states. Voters with no college education were 18% in both 2012 and 2008, about in line with New Hampshire 2016.
Time of Decision
17% of 2012 voters decided the day of the primary, 38% the prior few days, and Newt ran away with them by 20-point margins. 2008 featured less of a dramatic break - 18% decided the day of the primary, breaking slightly for Huckabee, and another 29% within the prior week, those being won by McCain. More than half of South Carolina voters in 2008 decided more than a month in advance, compared to half that in 2012.