The chart should say Percentage that voted for someone other than Ted Cruz. There were multiple candidates on the ballot.
Currently, RCP average shows that only 35.7% of likely Republican voters support Trump. http://www.realclearpolitics.com/epolls/2016/president/us/2016_republican_presidential_nomination-3823.html
If 64.3% of Republican voters don’t support Trump we have a big problem if we really want to defeat Hillary.
The RCP average hardly has any recent polls included. The HuffPost Pollster average, which includes far more polls, has Trump currently at 43.6% nationally.
http://elections.huffingtonpost.com/pollster/2016-national-gop-primary