So you actually think Mexico will pay for the wall?
I think if played properly they will.
Making up 20% of the world's GDP the american economy & US consumer has been the engine of the world's economies for decades.
We have a right to insist that other nations wanting to play in our sandbox not take advantage of their relationship with us as Mexico has. If our threat to level tariffs if they do not accommodate our request can be credibly made you can bet they'll come around.
Its not as if it represents a financial hardship for them.
Personally, with our current debt of 19 trillion I could give a crap who pays the measly 20 billion for the wall as long as it gets built.