As for "examples", take a look at those two books I mentioned. There are many more books, and many op-ed pieces every time Democrats lose elections.

It's only relatively recently that the more progressive wing of the party has said, "Hey, rather than try to bend over backwards to attract moderate conservatives, how about you garner more enthusiasm from your left wing?" Or at least, they've been saying it for a while, but were generally dismissed. I think 2016 made the proposition more thinkable: if they will vote for the Republican candidate even if he's obviously insane, maybe a new approach is needed.