More simply put, since many don't seem to understand, these are the criteria.
Fulfill one of the following three criteria:
1. Finish in the top 3 in Iowa.
2. Finish in the top 5 in New Hampshire.
3. Poll in the top 5 in South Carolina and fulfill one of the following four sub-criteria:
a. Poll 3% or higher nationally.
b. Finish 3% or higher in Iowa.
c. Finish 3% or higher in New Hampshire.
d. Poll 3% or higher in South Carolina.
Making the contenders:
Trump (1, 2, 3a, 3b, 3c, 3d)
Rubio (1, 2, 3a, 3b, 3c, 3d)
Cruz (1, 2, 3a, 3b, 3c, 3d)
Bush (2, 3a, 3c, 3d)
Carson (3a, 3b, 3d)
Kasich (2)
Option three is poll in the top 5 in an average of national and South Carolina polls and fulfill one of a-d. It's not just South Carolina polls that will be taken into account.