Our forthcoming book is titled Divided We Stand: The 2020 Elections and American Politics. Among other things, it discusses Trump's policies.
While manufacturing jobs declined from 32% of total employment in 1953 to 8.7% in 2015, manufacturing as a share of real gross domestic product has remained virtually constant due to increases in productivity.
As Mr. Trump found when he imposed tariffs on steel and aluminum, the resulting increase in jobs in those industries was small. This shouldn’t have come as a surprise: In 1980 it took 10.1 man-hours to produce a ton of steel. Thanks to automation, that was down to 1.5 man-hours a ton in 2017, with some steel makers achieving 0.5. Jobs gained in the steel and aluminum industries after the tariffs were dwarfed by jobs lost in industries that use steel and aluminum in their manufacturing process, not to mention the jobs lost due to foreign trade retaliation.
The uncertainty concerning which industry would be hurt next caused private investment to decline across the economy. GDP growth, which had been accelerating in 2017 and 2018, fell 20% in 2019, from 2.9% to 2.3%, in line with the Congressional Budget Office estimates of the negative effect of the protectionist policies.
Protectionism even hurt manufacturing in the states it was supposed to help. According to the Bureau of Labor Statistics, manufacturing employment in Michigan, Pennsylvania and Wisconsin, which had increased in 2017 and 2018, started to fall in 2019 as the trade war intensified.