In the aftermath of the Oct.15 debate, Senator Bernie Sanders closed the gap between himself and front-runner Hillary Clinton.

The average of the last six national polls, as reported by realclearpolitics.com, stretching over a three-week period before the debate, Hillary's vote share in a Democratic primary was 44 percent. In the CNN/ORG poll right after the debate, she got 45 percent, not much change. By contrast, Sanders averaged a vote share of only 24 percent. But in the post debate polling, he surged to 29 percent of the vote.

Since July 15, 2015, Sanders ratings have gone from 23 favorable, 22 unfavorable to their current level of 41 favorable and only 29 unfavorable.

During the same time period, Clinton's ratings have been flat with her favorable/unfavorable rating unchanged since July at 46 percent favorable/ 50 percent unfavorable.

Even so, there is some evidence that Sanders' surge has run its course. In the CNN survey, taken after the debate, it was clear that Sanders had gotten his point across. Asked which candidate would be the best at bridging income inequality, Clinton was ahead by only 42-38. But, still, Clinton led Sanders by 16 points. It may be that Sanders has begun to approach the upward boundary of leftist voters in the Democratic primary.

On the other hand, there is significant demand for Joe Biden to enter the race. While he draws only 18 percent if the vote in the three way Clinton-Sanders-Biden field, 47 percent of the primary voters want him to run for president. Between defections from Clinton and on the left and Biden's appeal to the party's more centrist voters, Clinton could be in a lot of trouble.

And then there is the Obama factor. Blacks constitute 25 percent of the Democratic primary vote. Fifty percent vote for Clinton, 25 percent support Biden and only 7 percent go for Sanders. But if Biden runs and if Obama supports him, look for those numbers to shift dramatically, perhaps enough to nominate Biden.