20% would be a good number to compensate against somebody dumping subsidized crap on our shores. I tend to believe, however, that high tariffs as a rule do more harm than good, and that free trade (actual free trade, not managed trade) with friendly and neutral countries is beneficial to us.
As an example, the Smoot-Hawley tariffs (around 60%) and the resulting punitive tariffs on our goods by other countries, caused such a slowdown in international trade that it contributed to the Great Depression, due to a lack of foreign goods in addition to our domestic goods.
That Smoot Hawley significantly contribution to the Great Dispersion is neocon lie. Look at the raw data. Trade vs GDP? 4%. 4% which went to 2% of the economy post Smoot is not going to tank it in any significant way.
Dispersion = Depression