I am not sure that Cruz and Rubio supporters = Trump supporters either. On the flip side 85% of Bernie supporters say they like Hillary. As I said the spectacle of Trump(and all the media attention around him) has increased the numbers for the Republican primary. If Trump is the nominee I do think much like Rubio and Cruz in the primaries, Hillary will get alot of that negative Trump vote coming out in November(not saying she will get the Cruz and Rubio support, more a case that people who are lefties who might not show up if Rubio or Kasich was the candidate will show up to vote against Trump).
It's a basic case if Trump doesn't run, I don't think the Republican primary is nearly as large as it currently is(although probably higher then 2012)