It is important not to overstate the effect of things like the DNC email scandal. The pundit and political fandom classes are wholly unrepresentative of the nation. Probably 95% of the public could not tell you who Debbie Wasserman Schultz is. The majority probably could not even tell you what the DNC is. For these and other reasons, the scandal just cannot have that much of an effect.
Nonetheless, the scandal is still worth remarking upon because of what it reveals about a certain kind of pro-Democrat argument.
According to this argument, the Democratic party should be understood as a coalition between leftists and liberals, broadly speaking. Whereas in normal countries, you have separate left parties and centrist parties that then create external coalitions to form governments, the Democratic party is supposed to be a single party that contains the leftist and centrist blocs internally.
In a multi-party system, the left-of-center blocs compete for leadership of their coalition by seeing who can grow the largest party. The head of the largest party in the left-of-center coalition then becomes prime minister or leader of the opposition.
For the single-party coalition to work similarly, the internal blocs must be able to compete internally to see who has the largest internal support. And crucially, that internal competition must be fair. If the internal Democratic competition is rigged in favor of the liberals, then the leftists have no real reason to participate in the coalition. And vice versa.
Participation in the coalition is supposed to be based on the promise that the bloc you belong to has the ability to lead the government. But if the thumb is on the scale against your bloc, that promise is betrayed. Where the neutral arbiter of the internal competition is in the tank for the other bloc, you don't really have the ability to lead the government. All you end up doing is supporting the permanent leadership of the other bloc.
No doubt liberal partisans like the idea of a permanently impotent leftist bloc that they can nevertheless dupe into swelling the ranks of the Democratic party. But it is hard to see what leftist partisans get out of such an arrangement.