US Politics

In simple terms, they make imports more expensive.

Basically tariffs are a good idea for a developing country that needs to nurture its own industries to allow them to get to the point where they are competitive internationally. At that point you suddenly want everyone to get rid of tariffs so your now world-leading industries can access the global market.

When the US became independent the British said, 'let's have free trade - you send us the raw materials, we'll make stuff and you buy it.' The Americans said 'Fuck that, we will put tariffs on everything and develop our own manufacturing.'

After the war, the US set up the IMF and World Bank, who said to Europe and all the developing countries 'Let's all have free markets so your people can buy our stuff more cheaply'. The developing countries said 'but don't developing countries need tariff protection for their emerging industries to develop, or else they will be trapped as permanent exporters of raw materials at low margins?' WB and IMF said 'that's right, but if you don't want your people to starve / have sanctions / be invaded / have coups / etc - no tariffs.' Europe and dev world said 'ok then'

Now, the US can no longer compete internationally in many markets, tariffs suddenly look like a less bad idea. But it would mean that American manufacturing would gardually become less and less competitive globally (think cars) and only focus on their domestic market. In many ways it would be similar to the 1930s. It would be bad for Americans, but worse for virtually everyone else.

À lot of businesses import the things they sell so if you put tarrifs on China, for example, then that cost ends up being passed on to the American consumer in the end. You also have businesses buying lots of stock before the tarrifs come in to play, this takes money out of the economy because they've spent money they would have spent on hiring more staff or other things to improve their businesses to just tie up in stock.

The argument on the other side is that in the long run this should lead to those outsourced manufacturing industries returning, but the horse seems to have bolted on that one because people might say they want to 'buy American' but no-one is actually willing to pay what things actually cost for that reality.

Tldr, in the modern free trade system tarrifs just make everything more expensive.