2. It peaked at a time that nobody could credibly claim was the heyday of U.S. economic power.
Between the end of WWII and 1979, the US government took several actions that caused many manufacturing jobs to move elsewhere. The electronics industry that was booming in the US after WWII until around the mid '70s moved a huge amount of its production to Japan due to government action aimed at rebuilding Japan as a Cold War ally.
In the 1960s, Mexico set up its Maquiladora zone in northern Mexico aimed at attracting US factories and jobs with cheap labor and lax regulation. It worked, many plants were moved there well before NAFTA.
The US adopted many other favorable policies post-WWII to help rebuild Europe and other nations, actions that opened the US to cheaper goods and caused many US plants to be moved overseas, starting in the 1950s and '60.
we're also seeing employers all over this country complaining that they can't fill their open positions.
True, but that is a very recent development brought about by Trump's tax cuts, reduced regulation and his America First approach to trade.
Few still pretend that NAFTA did not cause a large number of US factories and jobs to relocate to Mexico, as well as attracting foreign plants which produce mostly for the US market. Reducing the tariffs were just an invitation for US plants to move to Mexico and export to the US.
I suspect automation -- not outsourcing -- has been the single biggest factor in declining U.S. manufacturing employment since World War II.
I also think the invention of the shipping container in the 1950s has had a far bigger impact on shifting trade patterns than most people realize.