No doubt. Parties are allowed whatever method they choose to select their nominee, including the party elites backing a popular insider.
However, we shouldn't confuse that with a democratic process. We should also recognize that such actions by the DNC would contradict their public statements to the contrary, that they intend to remain completely neutral in the primary process.
If the situation were as you claim, then the parties would not have much of an argument against stronger, populist 3rd parties, because the 2 candidates served to the voters in the General Election would no longer reflect a representative choice of American voters.
However, we shouldn't confuse that with a democratic process. We should also recognize that such actions by the DNC would contradict their public statements to the contrary, that they intend to remain completely neutral in the primary process.
If the situation were as you claim, then the parties would not have much of an argument against stronger, populist 3rd parties, because the 2 candidates served to the voters in the General Election would no longer reflect a representative choice of American voters.