i think its three fold:
1. trumps support, nothing matters to them. provided liberals are mad, they don't care. there is no bottom, pedophilia, treason, attacking POWs and veterans, they literally don't care. so his 35-40% support is baked in, there is no changing there minds.
2. democrats are amazing at fumbling the ball. i actually disagree that democrats should make it about the economy. "the economy" is this big nebulous thing, that for 40 years the republicans have been garbage at, and democrats have done really well, but somehow the perception is that republicans are better at it than democrats. thats a losing fight. democrats need to make the election about healthcare. its tangible. people's lives changed with the ACA was passed. the ACA is as popular as it ever has been, hell, medicare for all is super popular ... its tangible, its something the democrats are known to do better, and it can win. also republican scare tactics doesn't work well here, as we've seen the GOP's bag of tricks here, and we know they have nothing. literally nothing, no plan, no alternative, nothing. so the fear mongering game doesn't work, there is no MS13 or "libs just want more crime" bullshit.
3. where democrats will fumble the ball, will be in picking someone the fox news of the world can vilify well. it worked so well with hillary. she was a bit of a robot, sure, but the GOP and fox news knew for over a decade that she was going to run for president. and all they did was try to stick things to her. none of it was real, no murders, no Benghazi, her emails ... all pathetic ... but 10-12 years of constant "hillary is bad" programming made her bad regardless of the facts. democrats will pick someone fox news can define as terrible. and they will lose becuase of it. all they have to do is make the democrat seem kinda sketchy, and people will vote for trump again despite everything.
on the plus side, i think this is why its actually a good thing no "front runner" has been named ... keeps the years of bullshit to a minimum if they don't know who to attack.
and because of the electoral college, less than 100k people across three states picked trump over hillary! awesome way to measure the will of the people guys!