The party's largest elements are the Socons and the Fiscalcons ~ who together are at least 40% of the base ~ you have geographic groups, e.g. much of the Midwest, and religious bodies, e.g. everybody but jimmy Carter's Baptists, half the Catholics, Pentecostals, and so on. To a degree they are sufficiently different you have to think of them as separate groups ~ they may overlap the Socons but not as much as you imagine. They also overlap the business community.
There are dozens of different groups and movements within the Republican coalition ~ however, it's not so much the base that's a problem, but a group that is not part of the base ~ we've ended up calling it the GOP-e on FR. They are at most 15% if you count all their hangers-on and supplicants.