I mean there are lots of potential answers for this, but there are also some people who are probably going to be left behind and that sucks. That's also what the social safety net is for.
The thing is that these manufacturing jobs are going away because they are no longer needed due to automation. That's technological progress and it's a good thing. What America sucks at unfortunately is using the fruits of that progress to aid those displaced by it.
I don't disagree with any of this. But these are the problems that Democrats face when trying to convince those "unfortunate data points" in the middle of technological progress, that their plan is the best:
--You can offer them a social safety net, but many of them don't want it. They think of it as welfare, while they actually have a lot of pride earning their keep. This doesn't mean they are always judging people that are on assistance or always think that the lot of them are "welfare queens" (some do, of course), it is just that for them, personally, not working and receiving a simple pay check to keep you going is its own sort of prison. And this is the common criticism of welfare--depend on it long enough and it becomes a necessity. I think it does work better as a temporary program to aid people through transition, but that sort of model isn't going to fit everyone. And, well, welfare reform is a different discussion.
--They
are people, not data points. Displaced people are going to be righteously pissed when they are the victims of progress. No one today mourns the unemployed stagecoach-tilters or fragmented stable boy union c 1910-1920, but I'm sure they had a lot to complain about when the Model T started rolling out and no one was listening then. Eventually, that generation will pass as will the successive generation and again, no one will mourn the non-existent coal miners or steelworkers replaced by robots and cleaner, better energy sources. But right now, those people have to live through it and bring their children up into some new paradigm that their parents probably don't understand and can't predict.
The Democratic party hasn't had much of an answer for the generations caught in the middle. It doesn't help that the Republicans are running batshit though states like Wisconsin and destroying unions left and right. It used to be that the democrats were the party that had those worker's backs. You can argue that it was just republican legislature and power that let these things happen, but the reality is that the democrats, c. 1988, stopped being the populist working-class party that supported unions, and became their own brand of high-minded, consultancy-driven, big data elitists, applying republican-level thinking and solution-eering to their own demographic base. These voters stuck around patiently and, primarily out of loyalty, respect and generational memory, watched these new grand plans keep them happy enough. But by 2000 or so, when these communities started dissolving, jobs started leaving, Unions started their dissolution (hey--what happened to that party that at least would protect my job while their great plans would work to make a better life for my kids?), drugs and crime took over, I think they started to realize that these grand plans were never going to make their lives better. Modern, advanced jobs weren't showing up in their towns (but hey, they sure did improve big city life, didn't they!), and so naturally they start looking elsewhere.
Simply, the democratic party stopped caring for their core base. Offering them great solutions from afar and asking them to be patient while the solutions come along is not caring. It's the same empty promise of "trickle-down" stupid-nomics (and well, here we go
again with that one!

)