You have this backwards. The key to a democracy is voters. A political party needs voters. Voters don't need political parties. A political party can be narrow, supporting a narrow ideology and pushing out all dissent. Or, a political party can build a broad coalition.
Obama built a coalition, he invited in and welcomed women and minorities along with working class White people. He didn't pit one side against the other, and he welcomed people who disagreed with him on important topics to be a part of his coalition. After the election he continued to work hard to reach out to the other side.
Hillary did the opposite. She ran her gender. She ran away from White working class voters. People felt insulted by what she said.
The Democrats in 2020 can run an Obama like campaign... and they will earn my enthusiastic support. If they run a Hillary like campaign, I don't want to have to hold my nose again.
The voter is the key to a democracy. Political parties have to reach out to voters, the voters don't owe anything to political parties. If voters are feeling alienated by a political party... that isn't the voter's problem.
The Democrats have to earn my vote... that is if they want it. If the Democrats take your attitude toward voters, that the best way to get 4 more years of Trump.
Democrats 2020. If you don't like it, take a hike.