Total Votes in 2016 Election: 128,838,342
Total Votes For Trump: 62,984,828
Total Votes For Clinton: 65,853,514
Source: https://en.wikipedia.org/wiki/2016_United_States_presidential_election
Percentage of Obama Voters That Voted For Trump
“Estimates of the raw number of such Obama-Trump voters range from about 6.7 million to 9.2 million.”
6.7 divided by 128.8 = 5.2%
9.2 divided by 128.8 = 7.1%
Answer: Between 5.2% and 7.1%
Source: http://www.centerforpolitics.org/crystalball/articles/just-how-many-obama-2012-trump-2016-voters-were-there/