No protest after the Iowa caucus meltdown, no challenge to Perez to step down; his campaign bragging about winning IA's popular vote allowed more shenanigans. He never made an issue of Super Tuesday's voter suppression occurring, went along with electioneering in a pandemic, not calling for an halt to such an election but fully conceding the results; he passed up discrediting Biden as instigator of the Wall Street bailout, except for Sanders exposing Biden's Social Security lies.
Sanders could still seize the opportunity that has yet been gifted to him, even more than the debate, making a case that only his social welfare philosophy can meet the crisis of coronavirus and mobilize his adherents beyond pure electoral politics.
By not bowing down to party pressure to concede to Biden and endorse him soon, he could reshape the general election.
The force of his policy proposals was diluted by his association with DNC's message that Trump is the existential threat we face, not a discredited character like Biden behind every policy malfeasance that led to Trump.