Well, with an unpopular incumbent (and Hillary is basically viewed as an extension of Obama’s term, so she gets hit with this), the numbers almost always break against the incumbent in the weeks before an election. This happens regardless of any polling shenanigans that are going on.
When Obama ran in 2008 they were polling him with a d+8 weighting.
They are now polling Hillary with a d+12 weighting which means that they are implying the voters are so excited about Hillary that there will be +4 more democrats excited to vote for her than the Bamster. They are saying that voting for Hillary is even more exciting than voting for Obama. Really?