It's possible the idea that they ran a "not Trump" campaign is true enough, and that was part of the failure vs. being more to the left or vocal or any number of other things suggested. But the very fact that "not Trump" made people not show up and throw the election to him, or worse vote FOR him, says a lot about the state of the country.
I get it, people are hurting economically and somehow get blinded into promises that magic will happen. But Trump? Anyone voting this time around was around when he was in office the first time...are we that short memory? Yeah, we apparently are...repeating the same thing over and over expecting different results. And that can be applied to both sides, but one of them was the same guy.