Protectionism doesn't protect jobs (in aggregate)
A recent study by Lydia Cox showed that the steel tariffs imposed back in 2002-03 ended up doing more harm than good:
In this paper, I study the long-term effects that temporary upstream tariffs have on downstream industries. Even temporary tariffs can have cascading effects through production networks when placed on upstream products, but to date, little is known about the long-term behavior of these spillovers. Using a new method for mapping downstream industries to specific steel inputs, I estimate the effect of the steel tariffs enacted by President Bush in 2002 and 2003 on downstream industry outcomes. I find that upstream steel tariffs have highly persistent negative impacts on the competitiveness of U.S. downstream industry exports. Persistence in the response of exports is driven by a restructuring of global trade flows that does not revert once the tariffs are lifted. I use a dynamic model of trade to show that the presence of relationship-specific sunk costs of exporting can generate persistence of the magnitude that I find in the data. Finally, I show that taking both contemporaneous and persistent downstream impacts into account substantially alters the welfare implications of upstream tariffs.
And the same sort of result occurred when the US imposed high tariffs on Chinese imports. Here’s The Economist:
One reason why America levied tariffs was to encourage manufacturers to relocate there. Yet trade friction has in fact depressed business investment in America, suggests research by Mary Amiti of the Federal Reserve Bank of New York and others. The share prices of companies trading with China fared especially badly after tariff announcements. This reflected lower returns to capital and, by extension, weaker incentives to invest. All told, the annual investment growth of listed American firms was likely to have shrunk by 1.9 percentage points by the end of 2020. Aaron Flaaen and Justin Pierce of the Federal Reserve Board estimate that exposure to higher tariffs was associated with a decline in American manufacturing employment of 1.4%. The burden of higher import costs and retaliatory levies outweighed the benefits of being sheltered from foreign competition.