The chart above is from the YouGov Poll. The pink bars show support for the Democratic candidates between December 14th and 17th (before the last debate, and the purple bars show support for each candidate between December 22nd and 24th (after the last debate). Each of the two surveys questioned about 600 Democrats and Leaners nationwide.
Note that there is very little change from before the debate and after the debate. And what little change there was can easily be discounted because of the margin of error (which is probably in the 4 to 5 point range).
There's only slightly over a month until the first voting occurs in Iowa and then New Hampshire. This set of supports for each candidate has been fairly stable on the national level for a while now. Is there going to be a change before voting begins, or are we looking at how the primaries will go through Super Tuesday?