Third Way and David Brooks will explain it one way (a victory for the common sense center if Democrats win, proof that Democrats are out of touch with Real America if Republicans win) and they'll be the ones who have the microphones because that's how it works.
They'll also provide a caricature of the supposed lefty view of things, which is that lefties want every candidate everywhere to get their orders from some Brooklyn Marxist Collective or something.
And there are enough people running for office that you'll basically be able to tell any story you want to! Lefty candidate X lost, proof that the lefties are wrong! Corporate Dem Y lost, proof that the lefties are right!
I don't speak for the Online Left. I never did and now I am old and The Kids Today have taken over with their Snapchats or whatever, but the real Online Left critique of the Democrats was never that they need to run commies in every district. It went something more like this:
Policy and rhetoric aren't entirely separable, but...
On policy: A lot of what DC thinks is "centrist" had no relationship to what the median voter actually likes and polls prove that some very lefty things are actually popular! Not all very lefty things! It is true that politicians who run on certain very lefty things can cause problems for themselves even when those things are very popular because not pissing off the money people makes them less likely to spend massive amounts of money to oppose you. Most people like minimum wage increases but the people who will run $10 million in ads against you about other things do not. Pundits do not explain this wrinkle.
On rhetoric: Everybody "knows" Democrats are going to raise your taxes, force you into a gay marriage, mandate that you have an abortion, take away your car, give all your money to black people, bus in caravans of doom from Central America, surrender to ISIS, etc. Mushy middle types also like "A politician who knows what he believes and knows what he stands for." You can't really run from the caricature of Democrats, and if you do you sound like someone who won't stand up for his own side in argument. Not a good look. Better to embrace it and make it sound good. Maybe not the take away your car one! That'll really make people mad. Explain that, yes, you're going to give rich people's money to black people but also white people! Free health care for the poors and the not so poors! Also, running against your party ("I'm a different kind of Democrat!") works for one politician, it doesn't work if half your candidates are doing it.
tl;dr: some, not all, lefty policies are actually quite popular! Sound like you believe what you're saying and that everybody can have nice things instead of hoping "not quite as evil as the other guys" works. If people want evil they're gonna vote for the evil party. It isn't a secret which one it is.
