You want to create the left by destroying the left?
The current democratic party no longer represents the left. It represents the middle.
America, for the most part, is a conservative nation. In a way, by design. (I'm not going to give you a breakdown of US history, so you can choose to accept this or ignore it)
Why do you, a conservative, choose to vote for Democrats? After all, the Republican party is supposed to be the conservative party.
The problem is, what the republican party use to stand for, in the days of Eisenhower and Teddy Roosevelt. Isn't what the party stands for now under Trump. The change began under Reagan, or right prior to his election win.
The problem is, the republican party, in order to win elections, decided to give a voice to the extreme fringe right. The evangelicals, the westboro baptists, the klan, the white supremacists. That's who the republican party now represents.
Instead of conservatives fighting to kick that element out of the republican party (which, I don't believe they can), they're now fighting to transform the democratic party into a party that represents them.
For the Democratic party to represent you, it has to abandon the left.