The current favorite myth among the Establishment is that collectively, the support among voters of moderate candidates running for the Democratic Presidential Nomination, far exceeds Sanders' support by those left-wing, Pinko, whakos. Therefore (their reasoning goes) if there were just one moderate candidate in the field, and the moderate wing of the Democratic Party were not so splintered, then moderates would be rallying around that candidate, and easily beating Sanders.
Unfortunately, this is of course the kind of baseless, seemingly reasonable myth that gets a lot of traction in circles which need a myth because reality is not supporting their biases.
But, the fact is that in one-on-one national match-ups, Sanders actually does better than any, single moderate Democratic candidate running against him.
Sanders 48% - Biden 44%
Sanders 53% - Bloomberg 38%
Sanders 54% - Buttigieg 37%
Sanders 54% - Klobuchar 33%
In addition, in Nevada Sanders beat all of the moderate Democratic candidates in the race combined.
Candidate Votes CCD* CCD Pct. Del.
Bernie Sanders 41,075 6,788 46.8 %