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?
There is no rational reason to be weighting the Democrats positively in this cycle at all, much less to that degree. So, the only explanation is that they are doing it because that is how far they need to skew the polls to create the appearance that Hillary might win.