For this map, I found the percentage of each state’s total population voting for each candidate in all presidential elections from 2000 to 2016. The candidate who had the highest percentage (in any election year) is the “winner.”
I realize that it would be more ideal to use the actual eligible voting population, rather than the total population, but I have been unable to find that data further back than 2000, and I am currently working on a second version which will incorporate more past election years. So, for the sake of uniformity, I have gone with total population. I do not believe that this greatly affects the results, at least not in the 2000-2016 time frame.