At this time the most viable Presidential Candidates appear to be O'Rourke. Klobuacher, Newsom, Brown, and Castro. This will in all likelihood change but at this early stage, these would probably be the most appealing candidates to consider,

https://www.cnn.com/2018/12/26/politics/democrats-2019-decisions/index.html?fbclid=IwAR3XxhRt0oZFmrYn4BIRoIu2Kls92CiTuPv0dcndF-LvfLM-jm09hVHLVh4