The quick math on Trump's latest proposal
In 2015, the United States imported $295 billion worth of goods from Mexico and $22 billion worth of services. That's $317 billion in total imports. A 20% tax would raise $63.4 billion.
The cost of a wall is estimated at $15-25 billion. So in one year, you could raise enough to pay for up to four walls. It's also more than the entire annual US trade deficit with Mexico.
Now, you have to imagine that trade would drop pretty dramatically with a 20% import tax but over a few years it would still be far, far more money than you would need for a wall. You also have to imagine that this is Trump's idea of an opening salvo from his master-negotiating technique.
His problem is that he's just going to raise prices on Americans by making imports more expensive.
The Mexican peso doesn't even seem to be taking this comment seriously because it's kicking slightly higher at the moment.
Update:
Here is the quote from White House spokesman Sean Spicer and it certainly adds some confusion.
The $50 billion number there, presumably, is the trade deficit. But Trump said that tax would be on all imports. So it's not clear exactly what would be taxed because you can't tax a deficit.
