But as Mexico has pointed out, the Americans of course have every right to do whatever crazy thing they want, as long as it's on their side of the border and they pay the bills.
That's not good enough for Trump. To satisfy his need to be seen as a strongman, he wants to make Mexico publicly grovel. He needs to make the Mexican government humiliate itself before the world and before its own people, throwing away any vestige of national pride, by agreeing to pay tens of billions of dollars for the American wall that it doesn't want.
There's also the matter of practicality. Mexico's economy is 13 times smaller than that of the United States; its government budget is already under immense pressure in large part because of the collapse of international oil prices, with social programs, pension and education spending being slashed. Demanding that it cough up tens of billions of additional dollars to pay for a vanity project for a crazy American president is asking a bit much.
But hey, this is Trump at his bullying worse, picking on a much smaller, weaker opponent to make himself look bigger. It's also stupid. According to White House spokesman Sean Spicer, if Mexico won't pay for the wall directly, Trump proposes to do so by levying a 20 percent tariff on all goods imported from Mexico.
That punitive tariff would have to be approved by Congress, which is highly unlikely. And if it were imposed, the tariff would be paid by American consumers, not by Mexicans. And yes, it would indeed harm the Mexican economy, potentially putting millions of people out of work and making them desperate for a better life somewhere else
Gee, I wonder what would happen then?