Voting in the primaries is a clear indicator of who people are willing to vote for, what the demographics are, and even why people are voting for who they are in the exit polls. 99.9% of the time, the GOP will choose the candidate that more people are voting for because that translates to the best chance of winning the general election, which is the ONLY thing they are concerned with.
In the case of Trump, he has strong support within the party (which still baffles me) but he will get almost no moderates and in general matches up poorly with Hillary, and could very well permanently damage the GOP brand.