The USA are not the world. Even if suddenly they managed to taxe all the carbon in their economy, and all imports coming into their countries, you cannot force the world to follow.
China, Russia and India exchange massively between them, with Europe, Africa, and internally. Those product would be cheaper, since no carbon tax, so no incentive.
It's a hard problem to solve.
If we get a big hydrogen market, the problem never needs to be solved.
Banking on all politicians in the USA and Europe to vote and maintain forever a carbon import tax is a big bet.
And it won't affect exchanges of goods between Asia, Russia, South America and Africa, or internally in each country lika China or India. Internally use goods will not be taxed, and be cheap, so they will import less, use more internal good, and pollute more.
I mean, of course you have to track where the methane came from but that’s pretty easy.
There are also ways ways to make hydrogen that emit lots of co2. So either way you have to track and tax.