[rebuilder]

It's an import tax he's talking about. Presumably the idea is that US producers will gain from decreased Mexican imports. How that will help pay for the wall I don't know.

Honestly, I'm not sure it's worth it trying to analyze Trump's policy at this point. He seems to have taken a page from the Russian playbook, in that he seems intentionally chaotic and unpredictable, in order to keep the opposition reactive.

[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.