Donald Trump could instigate a trade war. On March 8, he took the first step by suggesting steel imports are a threat to national security and applying a 25% tariff on them.

While the president has said that "trade wars are good, and easy to win," the history of protectionist measures suggests there will be economic pain on all sides. The US has a number of soft spots that trading partners can target by placing tariffs of their own on vulnerable American goods.

Eight of the largest international markets subject to the US steel tariffs account for about 40% of the US's exports. Shown here are the 4,304 category-market pairs where the US exported at least $10 million of products to the EU, Japan, South Korea, Switzerland, China, Brazil, India, and Russia in 2016. (For now, Canada and Mexico are exempt from the tariffs, so they are not included in this analysis.)

We've arranged these products into a grid measuring how much the US relies on an individual partner to buy a product along one axis, and how much the partner relies on the US to supply it along the other axis.

A tariff on a product that the importing country relies heavily on the US to supply wouldn't be advantageous to tax at the border.

But a tariff on something that a country imports from all over, but accounts for a large share of US exports of that product could make a perfect target.

Explore for yourself the products that could be targeted in a trade war against the US.

imported of in 2016, accounting for of US exports of the product and of ’s own imports of it.

Note: Items listed at more than 100% are due to differences in exporter and importer categorization and valuation standards.

Data: International Trade Centre

Of course, certain products are irreplaceable. A tariff on American wine, for instance, would hurt a nation's citizens who enjoy California cabernets more than a tariff on American corn, since nearly identical maize can largely be sourced from elsewhere.

Furthermore, certain items are more important than others to a nation's productivity. A country that makes lots of clothes may need to import lots of fabrics. A tariff on fabrics, then, could hurt the importer more than the exporter.