Where Did All The Purple Go?

After the 2016 presidential election, a good deal of conversation was dedicated to American's increasing political segregation. Despite the focus, I couldn't find a map that compared 2012 and 2016 election results using the same colors and brackets. The number of Americans living in "purple" counties (with vote margins of less than 10% in either direction) shrank over 15% between 2012 and 2016, from 79 million people to 67 million people. The number of "purple" counties shrank from 557 to 326. I created this map in QGIS using data from townhall.com and the National Atlas of the United States.