According to CNN exit polls the Republican frontrunner, Senator McCain, has not won amongst self-identified Republicans in any of the primaries yet. Despite that he is the presumptive nominee. In NH he lost the Republican vote by 1 point, in Michigan he lost by 14 points and here in South Carolina and down in Florida he tied for the Republican vote.
Now that the field is clearing he'll win a plurality of Republicans somewhere on Super Tuesday but as of now the probable nominee of the Republican Party has yet to carry the self-identified Republican vote in any primary.
H/T Rich Lowry at The Corner