From the Gallup Organization:
But even as prominent Democrats admonish the Vermont senator, who only recently joined their party, U.S. adults who identify as Democrats or lean toward that party continue to have a broadly positive view of Sanders. Plus, he continues to be significantly more popular than Hillary Clinton. Sanders’ current net favorable rating among Democrats (+52) outpaces Clinton’s (+39) by 13 points. This is significantly different from early May, when Clinton’s and Sanders’ images among Democrats came close to parity.