Or, as Reuters themselves put it: Sanders can't break through against Clinton.
Here's a chart showing the preferences of likely Democratic primary voters over the past couple of months in the Reuters online poll. As of Friday October 2nd, it's Clinton 58%, Biden 19% and Sanders 17%. You read that right: a whopping 39-point lead over her nearest competitor.
As you can see, it's generally been fairly stable...but not always. For instance, notice the slow and steady Sanders surge around mid-September? That was about the time that Quinnipiac came out with their much-publicized poll which showed Bernie leading Hillary by one point in Iowa and the general "Hillary Doom" theme was reaching its apex in the media.
Now check out the huge one-day spike towards the end for Clinton. That was on Wednesday September 30th. Something to keep in mind is that this is a five-day rolling average poll...so it seems as if something particularly dramatic might have happened right around then. What could it have been?
It just so happens that last Wednesday was when the Kevin McCarthy thing really blew up after his nationwide admission the night before about the purely political nature of the Benghazi committee. And it looks like Democrats noticed big time.
It should also be noted that this past weekend, which included the very widely-viewed SNL appearance which capped off her best week ever, is not yet registered in this poll. So no one should be surprised if Hillary's support in the polls goes even higher in the coming days.