In the first three early-voting states, Republican turnout was up from 2008 — just slightly in Iowa and New Hampshire, but significantly in South Carolina, where it jumped by 35 percent.
The pattern did not hold in Florida on Tuesday. With nearly all of the votes counted, Republican turnout is about 1.7 million. By comparison, just under 2 million Republicans voted in Republican primary there in 2008.
Part of the reason for the difference may be that a ballot measure, the Florida Save Our Homes Amendment, was on the primary ballot in 2008 and could have encouraged turnout even among voters who were not interested in presidential politics. In addition, the Republican race in Florida was closer in 2008 than in 2012, which usually improves turnout at the margins.
Still, this is not a great result for Republicans — especially after their tremendous success in 2010, a cycle during which Republican turnout was extremely high and contributed to the party’s 63-seat gain in the House of Representatives.
And the results are somewhat worse for the G.O.P. if you look turnout only among voters who identified as Republican in exit polls in the early-voting states. This is arguably the more relevant comparison because Democrats do not have a competitive nomination race this year, freeing up voters who might have voted in the Democratic primary to vote in the Republican one instead.
(Self-identifying as Republican is not the same thing as being registered as one. In Iowa, for instance, participants in the caucuses must be registered as Republicans, but they can change their registration at the caucus site — becoming, in essence, Republicans for a day.)
Among Republican identifiers, turnout was down by 11 percent in Iowa, by 15 percent in New Hampshire and by 16 percent in Florida. It is also down by 10 percent overall through the first four voting states.
The clear exception was South Carolina, where turnout among Republican identifiers rose by 20 percent.
South Carolina, of course, was the strongest state for Newt Gingrich. In contrast, turnout among Republican identifiers was down for Mr. Romney’s two victories so far, as well as for his near-win in Iowa.
It is not entirely clear what implications this has for November. Rallying the party base is often easier than persuading independent voters, and levels of voter engagement sometimes become clear only late in a presidential campaign.
At the same time, Republicans cannot be taking anything for granted despite their success in 2010.
Turnout at the midterm election has historically been a poor predictor of turnout at the next presidential election. Democrats had a relatively strong turnout in the midterm elections of 1982, but a very poor one in 1984, contributing to Ronald Reagan’s landslide victory. Republicans had a strong turnout in the 1990 midterms, but in 1992 Democratic and independent voters tended to be more enthusiastic.
So just because Republicans had a strong turnout in 2010 is no guarantee of a repeat performance. Mr. Romney is in an excellent position in the Republican nomination race, but he may still have some work to do in motivating his base.