http://www.nbcnews.com/meet-the-press/56-percent-democrats-not-concerned-about-finding-clinton-challenger-n353261

But to be fair, let's put those percentages in a better perspective.

In telephone surveys
31% of voters identify themselves as Democrats.
26% identify themselves as Republicans
42% Identify themselves as Independents.

56% in survey results x 31% who identify as Democrats = 17% of the voters.