Ezra Klein recently wrote an opinion article ("Why Democrats Still Have to Appeal to the Center, but Republicans Don’t") that argued that conservatives form a monolithic block and the US that is favored by the electoral system in a number of ways. And that to deal with that the Democrats should take a position a bit right from the center to cover enough people.
There is a lot wrong with this position. First of all, the right isn't monolithic. Look at other countries and you will see conservative parties that get nearly half of the vote only in two-party systems like the US. Conservatives have their own divisions. It is a kind of wonder that deeply religious evangelicals vote for such an immoral man as Trump. It is because they feel cornered. Do remember that case of the baker who refused to make a wedding cake for a gay couple and got in trouble for that? It crosses the boundary of live-and-let-live. It dehumanizes people who believe that gay marriage is not a good thing - until very recently a wide majority of the US population.
Any European politician who has had a look at the US will confirm that what in the US is called "moderate" would inside Europe be considered extreme right. The Democrats have already been following Klein's advice for many decades. And the results don't confirm the claim. Obama was to the left of Clinton. Yet he won elections and she lost. And the fact that many poor Democrats have voted for Trump while they might have voted for Sanders is he had been a candidate belies the claim that politics can be explained with a simple left-right continuum.
Politics is about ideas. But "moderate" Democrats don't have ideas. Their economic and defense policies are almost indiscernible from those of the Republicans. They are in fact a light version of the Republicans. And when people get a choice between a light version and real thing many choose the real thing - specially in times of discontent like we have now.
Many of the ideas of Sanders aren't that radical. If they would have been proposed by someone like Biden they would be widely embraced. But where someone like Sanders is focused on ideas on how to make the life of the common voter better Biden is primarily focused on pleasing his sponsors and not rocking the boat.
Many Democrats are amazed that Trump is getting away with so much immoral acts and lies. But what people like is that he is someone who stands for something - even when he faces criticism. That is what they like about Sanders too. And that was were Warren made a big mistake when she adapted her Medicare plan after criticism. Sure, if Sanders wins the elections he will have to negotiate with Congress to get his plans adopted and he might very well end with the kind of plan that Warren is proposing now. But that doesn't take away the fact that his present proposal is sound and defensible. Warren is ceding ground before the fight has even started.
What are Democrats like Biden really standing for? They like to spend a bit on social issues to keep people happy but they are afraid to make any structural changes that might get criticized. They like to criticize countries like Russia. But that looks suspiciously like yet another type of foreigner bashing - not that different from racism. They like also to go to extreme lengths to defend gays and transgender rights. But result looks a lot like the bashing of "deplorable" poor whites and evangelicals.
Parties that don't have plans to make people enthusiastic for are bound to focus on demonizing people instead. The Democratic Party has been falling in that trap. Unfortunately its leadership still seems to be unaware of the problem.