I am curious why Sanders' numbers continue to improve so steadily in this type of polling.
IIRC last week Rubio was on top of a match-up with Sanders by +3. That's a pretty big swing in one week.
Side observation: Trump's national numbers are generally slumping. My working theory is that Trump supporters are going to Sanders, in at least comparable numbers as to the other Republican candidates.
That other thread, where Trump mistook Sanders' campaign for his own, is insightful.