[rebuilder]

Ok, having done a bit of morning reading, I'm inclined to think the tax is a red herring. This is about the wall. Trump wants to get started with building it, maybe to be seen keeping his promises, maybe because it'll employ US workers. But it's expensive, so he needs some story for how it's going to be paid for, specifically how Mexico will pay for it. Even if that doesn't pan out, by the time it's clear the cost was paid by the US taxpayer, he'll have moved onto bigger things that will distract from the issue.

Alternatively, I'm wrong, and the wall really is just a huge put-on, used as leverage against e.g. the mexicans, or part of a more obscure campaign.