The US has always argued for other countries to reduce their tariffs. Here's an article from 2002, for example: https://yaleglobal.yale.edu/content/obstacles-zero-tariffs

"The fact is that there is a strong feeling in the developing world that trade rules do not apply equally. Indeed, Washington lost the moral high ground earlier this year when it slapped steep tariffs on steel imports and locked in subsidies for its farmers. As well, the US has in place a sophisticated regime of non-tariff barriers such as anti-dumping laws that exporters from developing countries have found difficult, if not downright impossible, to circumvent. "

(The "non-tariff barriers" are important - all kinds of environmental and safety standards could be considered as these, and they can be far more difficult to deal with than simply paying an import duty. This is another thing a lot of Brexiteers haven't realised)