I'll bite, even though I really shouldn't.
How do you define "average living standard", so that it would take a colossal disaster to have US reduced to that of Poland?
In terms of nominal GDP per capita, the US is around $85k with Poland at $25k, so US GDP would need to fall around 70%, which would be an unprecedented fall, the kind historically only associated with mass bombing or extreme hyperinflation.
In terms of nominal GDP per capita, the US is around $85k with Poland at $25k, so US GDP would need to fall around 70%, which would be an unprecedented fall, the kind historically only associated with mass bombing or extreme hyperinflation.