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The way US has been ruined by this pandemic makes me wonder is actually US had a solid economy or they just hide their vulnerabilities to make themselves look strong. I also think some poor decision making is also responsible for the fall of economy though.
Very true.
The Economy they were focusing on, namely the stock market, was already decoupled from the real economy. The highly capital intensive american firms (banks, hi tech in the first place) weren't able to trickle down their success in the real economy (bar San Francisco tenants, of course).
Unemployment running at historical minimums and payrolls report from BLS positive since a decade were also hiding slack labour force and partial hiring.
The pandemic toppled this precarious equilibrium, and pushed the two economies in a exploding wedge: while common people was made even poorer, the rich became even richer.
Who to blame? of course the central bureacts, who weren't even able to prepare for the pandemic arrival: they saw it in China, they saw it spreading in Europe, but they weren't preparing, thinking a magical wall would protect them. When the reality hit, they were slow to respond.