MoveOn, a liberal, internet-based group, will not win Bernie Sanders the election because they fail to broaden Sanders political base. Both Sanders and MoveOn are viewed as firmly entrenched in left field. Sanders currently appeals to progressive, left-leaning voters but cannot win the election without the support of undecided voters and middle-of-the-road Americans.
No, MoveOn's endorsement shows promise for the Sanders campaign, but it in no way ensures a Bernie Sanders victory. While approximately 78% of 340,665 MoveOn voters agreed to the Sanders endorsement, only a small number of voters is represented by this fact. That is not to say that Bernie Sanders will not win the election. If anything, this endorsement proves that he has a very real chance of winning. Although the endorsement serves as a huge boost to Bernie Sanders, it cannot be solely attributed to a Sanders victory.
I happen to agree with Bernie Sanders on much of his platform. Unfortunately, from a practical standpoint, the political climate is such that if Democrats are to be successful, they need a more mainstream candidate. Hilary absolutely has many detractors, but she is a bit more firmly in the public eye. Bernie Sanders would need a ton of grassroots support, more than just MoveOn, to raise his profile and win the nomination, let alone the election.
It's still too early to say who is going to win, but there is no doubt that MoveOn's endorsement will help Bernie Sanders win the primary over Hillary Clinton, and could help win the election. MoveOn is very influential with progressive voters, but their endorsement could actually hurt Sanders in a general election by forcing conservative groups to fight back.