The endorsement and campaign event was critical for Clinton as she seeks to bring Sanders's anti-establishment supporters into the fold as some polls show presumptive Republican nominee Donald Trump closing the gap and potentially making the presidential race a nail-biter.
The latest NBC News/Survey Monkey tracking poll has Clinton up just 3 points on Trump. The poll found that 82 percent of Americans felt it was inappropriate for Clinton to use a private server for her email while at the State Department. Somewhat amazingly, 20 percent of Clinton's own supporters said they disagreed with the Justice Department's decision not to prosecute her over the email setup.
Those figures highlight the critical importance of a full-throated Sanders endorsement and a significant campaign role for the Democratic primary runner-up. Sanders regularly ripped Clinton during the campaign as an untrustworthy creature of the establishment backed by Wall Street. The attacks won him a strong following, especially among younger voters who have not warmed to Clinton.
The presumptive Democratic nominee already has strong support from key parts of the Obama coalition including African-American and Latino voters. But she continues to struggle with younger voters whom she will need to turn out in significant numbers to win in November. A new GenForward poll found that only half of Sanders' young supporters are now willing to support Clinton.