Wow...
So, lets look at the actual data...
http://www.lynnvavreck.com/Site/The_Upshot_files/UPSHOT_Crosstabs.pdf
“Do you approve or disapprove of the executive order which … freed all slaves in the states that were in rebellion against the federal government?”
Trump: %20.5 disapprove
Rubio: %5.1 disapprove
Clinton: %6.2 disapprove
Sanders %9.8 disapprove
Now, the poll had 1983 respondents, so it's margin of error is ~2.2% so the 'disapprove' numbers for Rubio and Clinton are within the overall poll's margin of error... but its actually more complicated than that...
A common mistake in the reporting of poll results is the application of the margin of sampling error for the entire poll to various subsets of the population: women, men, Democrats, Republicans, independents. But each of these subgroups is smaller than the total group, so the margin of error is actually much greater. “A lot of journalists don’t understand that,” Berinsky says.
http://news.mit.edu/2012/explained-margin-of-error-polls-1031
If you are trying to use these numbers to assign statistics to the question "What percent people claiming to be supporters of _______ disapprove of the emancipation proclamation?"
then we have the following results - the margin of error for each result is given in parentheses:
TRUMP: %20.5 (4.8)
Rubio: %5.1 (8.66)
clinton %6.2 (4.35)
Sanders %9.8 (4.04)
You can't really say ANYTHING about the supporters of Rubio vs Clinton vs Sanders, but you sure can say something about the folks supporting Trump...