It is important to look at the arguments for tariffs in the Great Depression era of the 1930’s if we are to understand the full danger they bring to the world. 

In modern times, the basic argument against tariffs is, of course, the complexity of the world we live in. Something labeled made in America may have parts from different nations. Same holds true with something made in Mexico. But in the days of the Great Depression, the complexity did not exist. 

But in the Great Depression, the issue was a simple one. Tariffs are difficult to roll back. They cannot be applied temporarily. Of course, the argument that they could be applied temporarily was made by John Maynard Keynes, British economist, and the most influential economist of his time. keynes was a free trader who saw the need to modify his views as the Great Depression became to wear on. 

Yet he was opposed to trade deficits and viewed tariffs as a means to offset imbalances in trade. Keynes preferred devaluation over tariffs, and the turmoil caused by his rejection of free trade soon became a non-issue. From the article cited above entitled Keynes and Protectionism:

Keynes did not have an extended opportunity to respond to critics because the tariff debate was soon cut short and rendered moot by events. He had endorsed tariffs under the assumption that an alternative option, devaluation, had been ruled out. As it happened, just days after his September 1931 newspaper article repeating his call for tariffs, the British government abandoned its commitment to the gold standard and sterling depreciated sharply on foreign exchange markets. In a letter to the Times shortly thereafter, Keynes promptly dropped his call for a tariff… 

So, back to modern times, we can see that it is difficult to read investors in their reactions to tariffs. Stocks have been weakened but there has been no wholesale flight away from the market. That could come, but it is likely that investors are waiting for a signal that Donald Trump seeks long-term tariffs. That may turn out to be the case, but National Association of Manufacturers President Jay Timmons has said: