Tariffs are great for developing countries. It protects their nascent industries/businesses that are not even ready to compete with those from developed countries and specifically to prevent developed countries from dumping goods (look up anti-dumping laws). Tariffs suck for developed countries as it just raises tax on its own citizens without any benefits that are enjoyed by developing countries.

> being the devil when the US implements them, and being double-plus-good when the European Union implements them (or China or South America).

You can also flip the argument and say that it is "double-plus-good" when USD is reserve currency but is the devil when Euro, Yen, Yuan, Rubles, Rupee et all want to be reserve currency too. Why does US admin go bananas when the topic of a BRICS currency is brought up?

Developed countries have levers. Developing countries have levers too. That's how balance has been maintained all these years since the World order was established post-WW2. Now if US wants to undo this World order (which it itself help setup) and wants to behave like a developing country, then developing countries will encroach on areas US holds dear to it: USD as reserve currency, cross-border transactions through SWIFT, imposing sanctions etc. Remember that it is not US alone that holds all the cards. Everyone else has their own cards as well.