This is a chart of real GDP (total output of goods and services) divided by the Civilian Labor Force. We know that the labor force has been declining and is at, like, a
40 year low. Despite that, however, the output of our economy has never been higher.
What this implies is that fewer and fewer people are reaping or participating in the wealth thrown off by our economy.
Soon we will have robots doing most of the work. And then what? On the one hand you will have even greater efficiencies (robots don't tire, need to be paid, take vacations, etc) and, therefore, even more wealth being produced.
On the other hand you will have lots and lots less people reaping the benefits. So, are they left to starve? Live in the streets? Go without medical care? Walk around naked, without transportation, electricity, heat?
This is not just a looming crisis for the United States, it's a looming crisis for mankind. The only way to avoid this is for people to be guaranteed minimum levels of income with which to consume some of this output. Otherwise, there will be human misery and chaos everywhere. The world will look like Mel Gibson's post apocolyptic movie,
Mad Max.