From Uppity Negro at The Intersection of Madness and Reality:
Because the administration of Trump was a veritable dumpster fire even before the inauguration, the Democrats never had the usual trial by fire and public shaming that the losing party normally gets. There was never an opportunity for the Democratic party to listen to its constituents and perform a full autopsy on just how catastrophic the 2016 election was. Rather, an obstructionist-lite position was adopted, and the Democratic base hasn’t raised much fuss.
Most sane people are able to admit there’s no real way to say definitively that Sanders would have beat Trump in a tête-à-tête, but there was a particular resignation amongst the Democrats who held their nose, pragmatically voting for Hillary Clinton in hopes of keeping Trump out of the White House at all costs. For many, this wasn’t about making the decision to participate in electing the first woman to the presidency, but really about a clash of ideologies. Many Democratic voters were miffed at how little the party’s establishment reached out to Sander’s supporters. Unlike how Obama reached out to Clinton in 2008. While the numbers bear themselves out–Clinton did win the nomination fair and square–once the emails of the DNP were leaked it was clear that throughout the primary, every lever was moved to make sure Clinton secured the nomination.