Crowded primaries and a dedicated base
Re-posted from Facebook:
Democrats have the same situation with Bernie Sanders that Republicans faced in 2016 with Donald Trump. The field is far too crowded, so Sanders' base will win him primaries with 25% to 30%. The only way to stop Sanders is for multiple candidates to drop out, leaving only one or two candidates to take on Sanders. In a two person race or a three person race, Sanders can be defeated. Splitting the non-Sanders voters among eight or ten candidates is a sure path to a Sanders nomination.