It seems as if the Bernie and Trump people need a history lesson. First there is absolutely nothing Democratic about the nomination of a party nominee by the political parties. They weren’t created that way and they are definitely not that way now. At absolute best now that things are decided by the election of delegates to represent voters at a convention it is somewhat more equitable, but it is still not a popular vote by just anyone who wants to vote.
No political parties existed at the time of the 1788–89 presidential election. Candidates were either Federalists, meaning they supported the ratification of the Constitution, or Anti-Federalists, meaning they opposed ratification. These groups were not established political parties, however, and were united in supporting Washington for president.
In the beginning, each state decided how its electors would be chosen and there was no participation of the general population for several years. The original desire by the founders was that there be no political parties. Needless to say this came to an end somewhere around the first time the Senate voted.
Once political parties of whatever name existed, they had only one purpose: WIN!! Nothing has changed since. Parties have come and gone, split, reformed, traded places on positions, formed third parties and disappeared. Still they exist for one purpose: WIN!! No matter how idealistic you might be on the issues, you cannot interfere with that one purpose.
Once this purpose passed to the states rather than the vote of the Senate, various methods arose whether by caucus or primary to establish the Party nominee in Convention. It still is not “democratic” in the sense that is understood by most people. All you get is the opportunity in November to vote for whomever the party people have decided is their candidate by whatever method they have chosen to come to that nomination decision.
If you do not like the people who the parties have chosen, there is only one way to change the system. Go to work and elect a school board and wait thirty years. The School Board becomes a City council becomes a County legislator, becomes a Congressional district, becomes a state office holder, becomes the person who draws Congressional district. In other words, do the work or forget about electing your ideals to office because those party activists are the ones who organize the caucuses and primaries, sit at tables for hours, and count the votes. Once everybody has said their piece, they get to be delegates, attend conventions, and supposedly do what you tell them to do for one vote and one vote only. After that, if there is no nominee, they get to put their thumb on the scale and you get what you get.
If you did not understand any of the above, go binge watch The West Wing. Start here and keep streaming.