Until that is broken and majority of people realize there are more than two parties, your best approach is going to be primarying and change within the party.
I agree 100%.
I just also think that best chance is now 0%, because we know that established Democrats stand for nothing.
Republicans stand for shitty things, but they do a better job hiding that they're just working for billionaires.
Edit: To be clear - I will continue to vote for the candidate my union representative endorses, and I hope others do, as well.
But I will also continue to encourage my union leaders to look outside the Democratic party to build a strong coalition.